fbi advanced rifle training for the observer sniper

8/13/2019 FBI Advanced Rifle Training for the Observer Sniper

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FirearmsTactical.com

Reprinted with Authors Permission

ADVANCED RIFLE TRAINING

for the

OBSERVER/SNIPER

Special Agent Urey W. PatrickFirearms Training Unit

FBI AcademyQuantico, Virginia


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Advanced Rifle Training for the Observer/Sniper

Table of Contents



1. Definition ................................................................ 1

2. Concept and Utilization.............................2

3. Capabilities...............................................................5

4. Internal Ballistics ............................................5

5. External Ballistics ......................................... 22

6. Terminal Ballistics......................................... 33

7. Optics......................................................................... 37

8. Support Equipment ......................................... 42

9. Basics of Marksmanship ............................. 43

10. Appendices.............................................................. 49


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1. Definition

The military definition of a sniper is"an individual highly trained in fieldcraft and marksmanship who deliverslong range, precision fire at selected tar-gets from concealed positions." Althoughaccurate for the military sniping mission,this definition is too broad in scope forthe concept of snipers in law enforce-ment.

Military snipers act independentlyagainst a wide variety of both specifiedtargets and targets of opportunity. They

need not be concerned with questions ofauthority to act, criminal and civil liabili-ties, innocent bystanders, or the necessityto justify their actions in court after thefact. They operate in a hostile environ-ment in which friends and foes areclearly delineated.

Military snipers will generally en-gage targets at extreme ranges in orderto better avoid detection and counterac-tion by the enemy. Thus a military sniperneed not be concerned about the effectsof shooting. A killing shot is as good as awounding one. Either will remove anenemy from action. There are no hos-tages or victims whose welfare would beimperiled by a miss or a wounding shot.Further, identification of the target is notas critical as it is in civilian law enforce-ment.

In war, everyone on the other side ofthe line is an enemy against whom theapplication of force is proper. Destruc-tion of the enemy is the goal, and to at-tain that goal military force is brought to bear against both the enemy and the en-vironment in which the enemy operates.

In addition to shooting, the militarysniper's mission includes a function that isshared in its entirety with the law en-forcement sniper. This is the observationand reporting of intelligence, a functionwhich is crucial to the success of law en-forcement operations.

By virtue of training, position, and op-tical equipment the sniper has the bestvantage point and ability to observe andreport activities and information aboutsubjects, hostages, and the locations inwhich they are situated. This intelligencehas unique value to all facets of crisis

management in law enforcement, includ-ing assault planning, negotiations, anddecision-making.

Accordingly, the mission of the sniperin law enforcement is more specific anddetailed. It must account for the need tooperate in a friendly civilian environmentin which indiscriminate destruction is notallowed. It must account for the responsibility to act in a manner that does not un-necessarily endanger the lives of hostagesor bystanders. It must account for theneed to operate within the law and havethose operations subsequently reviewedin court. Further, the law enforcementsniper must be absolutely sure of theidentity of any target to be engaged.

The requirement for absolute identifi-cation is the single limiting factor that

governs the range at which the law en-forcement sniper can reasonably be re-quired to engage a target. Although themarksmanship skills necessary to hit aman sized target at extreme range arereadily taught, positive identification isdifficult if not impossible at ranges in ex-cess of 200 yards.


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The law enforcement sniper is an in-dividual highly trained in marksman-ship, field skills, and observation whodelivers precision fire on positively iden-tified targets ONLY upon command fromlegitimate authority. This individual iscalled an Observer/Sniper.

2. Concept and Utilization

The Observer/Sniper is an integralelement of Specialized Weapons andTactics Training, and as such is a vitalpart of crisis management. Crisis manag-ers are taught to take two immediate ac-

tions in the event of a crisis such as ahostage situation or barricaded subject.These actions are to deploy Observer/Sniper Teams and initiate contact withtrained Hostage Negotiators.

The immediate deployment of theObserver/Sniper Teams is twofold inimportance. First and foremost, fromtheir positions and with the opticalequipment available to them, they cancollect and relay vital intelligence aboutthe situation. The primary intelligenceobjectives are to identify all the playersin the crisis situation; to identify any andall weapons and explosives; to developgroup and individual profiles includingpatterns, locations, and tendencies; andto analyze the crisis point.

The greatest errors committed by Ob-server/Sniper Teams are failing to reportwhat is seen in complete detail; failing toreport the intensity of observed activity;and failing to utilize the optics. There is atendency to try to be too physically closeto the target area.

Examples of the specific intelligenceavailable are listed in the table below.

Examples of SpecificIntelligence

Subject descriptions

Hostage descriptions

Subject/Hostage locations

Weapons

Entry points

Location description

Construction details

Photographs

Activities

Patterns of behavior

Avenues of approach

Avenues of escape

Obstacles to approach

Booby traps

Alarm systems

Animals

Ventilation systems

Water suppliesPower sources

Flammable substances

Door/window details

An excellent, and often overlooked,role that can be played by Observer/Snipers is providing photographic intelli-gence from their advantageous positions.The more detailed the intelligence that isreported, the better and more effective arethe planning and subsequent actions ofthe decision makers in command.

Secondly, by putting Observer/ SniperTeams in place, the option of resolving theincident by sniper fire is available shouldinnocent lives be in imminent danger of


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loss and the option of tactical assault ei-ther unwanted or unavailable.

When a tactical assault is to be made,the assault teams will approach under

the covering surveillance and control ofthe Observer/Sniper Teams. In directcommunication with the assault teams,the Observer/Sniper Teams will advisethem when it is clear to move; when theyshould maintain position for fear of dis-covery; and if the element of surprise has been lost, order the assault executedimmediately.

The latter is called "Compromise" au-thority. Once an assault team has passedthe point of no return and loses the ele-ment of surprise prior to the assault, the"Compromise" signal keys the immediateexecution of the assault plan. The "Com-promise" signal can be initiated by anymember of the tactical unit who identi-fies the loss of the element of surprise.

Coordinated sniper fire can also be

utilized as a planned diversion for as-sault team entries, or against targets ofopportunity in concert with the entry.After assault team entry, the Ob-server/Sniper Teams are responsible foridentifying subject escape attempts; at-tempts at rescue or assistance by confed-erates or sympathizers outside thelocation; and hostage/victim escapes.

The reluctance of command authority

to authorize the use of Observer/ Sniperfire must be resolved prior to any actualutilization of Observer/Snipers. The kill-ing of one or more subjects can be per-ceived as an execution when done bysniper fire from distant and hidden posi-tions.

However, in actuality it is extensionsof the well accepted, and legitimate, pol-icy of shooting to protect life and preventgrievous bodily harm. Sniper fire should be authorized only in accordance withthat policy. Where feasible, and withinthe guidelines of protecting innocentlives, the utilization of sniper fire is farpreferable to making a tactical assault. Itis a tactically clean measure that does notexpose other officers and agents to therisks and hazards of a close range assault.

Prior to deployment several opera-tional matters must be defined relative to

the Observer/Sniper Teams. Teamsshould be thoroughly briefed regardingtheir missions for the periods before, dur-ing, and after any assault. Key times forsupply, relief, and rotation must be de-cided. Proposed initial positions must beidentified, as well as the locations of otherTeams and elements. Each Team must beallowed to select its own position, subjectonly to the needs of the mission as de-fined for the incident.

It is vital that the position chosen besufficiently close to allow effective obser-vation yet far enough from the site to in-sure concealment of the team. Positionsmust be at a sufficient distance from thetarget site to avoid detection and remainconcealed, yet close enough to allow posi-tive identification of targets and to assurea first shot kill. Communications and re-

porting codes must be standardized. Andlastly, the authority and rules of fire must be defined.

The latter is a critical matter. The au-thority to order sniper fire must be spe-cifically defined and invested in onecommand figure. There is no margin for


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any confusion among deployed Ob-server/Sniper Teams as to whether ornot an order to fire is duly authorized.Often, the tactical commander will be theindividual to order sniper fire after au-

thorization is given by higher command.This is done because the tactical com-mander's voice will be readily recog-nized and thus eliminate possibleconfusion over the validity of the order.

Further, rules of fire must be decidedfor exigent situations. Observer/SniperTeams must know when and under whatcircumstances they can fire. To illustrate:what if hostages are being harmed, orthe assault team is about to be am- bushed, or if outside confederates appearand threaten violence, or if subjects pre-sent the clear opportunity to fire? Theseexamples are a few of the issues thatmust be considered in establishing rulesof fire. As a guide, rules of fire should begrounded in policies of clear defense ofself and others.

An Observer/Sniper Team is com-posed of two men, both equally trainedin marksmanship, field craft, and obser-vation. The duty cycle for an Ob-server/Sniper Team should be fourhours in position, with responsibility onthe rifle rotating every 30 minutes. Theteam member not on the rifle is the pri-mary observer, log keeper, and commu-nicator. Time on the rifle is devoted tomaintaining the critical concentrationnecessary to make the shot no matterhow suddenly it might be ordered. Thatlevel of necessary concentration cannot be maintained longer than approxi-mately 30 minutes at a time.

Ideally, two Teams (four men) will beassigned each subject in an incident to better assure a killing shot should one beordered, and to better insure that eachsubject is in view of at least one Team atall times. In reality, that many trained in-dividuals are seldom available, nor is afour hour duty cycle always possible.

For example, in a Midwestern city apolice Observer/Sniper who made a suc-cessful shot had been in position by him-self for almost 12 hours before the shot.By his own account, the only reason hewas able to make the shot was because the

subject happened to peek out an openingat the precise moment the officer hap-pened to be looking there through hisscope. He had been authorized to shoothours before, but the subject nevershowed himself until that moment.

Realistically, almost all crisis situationsin the United States involving hostages orinnocent lives are resolved through nego-tiation. Accordingly, the intelligence func-tion of the Observer/Sniper Teams inconcert with the efforts of the HostageNegotiators is the most important func-tion of the Teams in actual situations.Nevertheless, the potential to resolve thesituation by sniper fire remains real andviable. The consequences of being unpre-pared, or unable, to exercise the requisitemarksmanship are severe. Sniper trainingmust emphasize skill and ability with the

rifle.3. Capabilities

Skill and ability with the sniper rifle isa matter of equipment, training, knowl-edge of ballistics, and expertise in the ef-fects of environmental conditions that can


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only be acquired through practice andexperience. The shooter and the rifleshould be capable of firing groups nolarger than one minute of angle (MOA)out to 300 yards as a minimum.

Accuracy with a rifle is customarilyexpressed in MOA. MOA is a unit of an-gular measurement that increases di-rectly with range. One MOA at onehundred yards is approximately equal toone inch, three inches at 300 yards, 10inches at 1000 yards, etc. For example, ifa group is fired at 100 yards measuringone inch in its greatest spread, then thegroup measures one MOA. If its greatestspread is four inches, it is a four MOAgroup. However, at 300 yards, a oneMOA group will measure three inchesacross its greatest spread.

It should be noted that groups aremeasured from center to center of thetwo most widely separated holes, andnot from outside edge to outside edge.The measurement is made from the out-

side edge of one hole to the inside edgeof the other. In groups clustered tootightly to allow this measurement to bemade, the measurement is taken fromoutside edge to outside edge at the wid-est point, and then the diameter of onehole is subtracted from the figure ob-tained. In this case, it is best to fire oneshot and measure the resulting hole forsubtraction rather than to simply sub-tract the bullet diameter.

Another way to look at it is that theMOA capability of the shooter and/orrifle represents the size of the smallesttarget that shooter/rifle combination canhit with certainty. Ideally, a one MOAshooter/rifle can hit a one inch target at

100 yards, a two inch target at 200 yards,or a five inch target at 500 yards, ignoringthe effects of other factors like wind,sights, and ammunition. Given a nominaldiameter of eight inches for a man's head,

a MOA rifle/shooter could expect tomake consistent headshots out to 800yards.

In actuality, the effects of factors suchas wind, sights, position, and ammunitioncombine to make 800 yard head shots ex-tremely difficult. At realistic law en-forcement ranges of 200 yards or less, oneMOA (or better) capability affords theprecision and certainty necessary to makea shot with confidence, minimizing risksto any bystander or hostage in close prox-imity to the target. In addition to havingthe skill and equipment to shoot oneMOA or better, the Observer/Sniper must be well versed in ballistics, external ef-fects, and the capabilities and limitationsof equipment and ammunition. All ofthese factors have interrelated effects onthe ability of the Observer/Sniper to

shoot accurately and consistently. Thefirst factors to resolve are the rifle and theammunition.

4. Internal Ballistics

Internal ballistics is the science of projectile motion within the rifle. More sim-ply, it is concerned with all that happenswithin the rifle from the instant of primerignition until the bullet leaves the muzzleof the barrel. Although its duration is inmilliseconds, the consequent effects uponthe inherent accuracy of the ri-fle/cartridge combination are major. Theeffects of the factors of internal ballisticsdictate the features of a sniper rifle andthe elements of its manufacture. Resolving


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these effects is the job of the gunsmith building the rifle. An understanding ofinternal ballistics begins with ignition.

Until the advent of modern "smoke-

less" gunpowder and the centerfire car-tridge design, firearms advances and ballistic development were relativelylimited. For hundreds of years blackpowder was the only gunpowder used.The powder charge was ignited by aseparate powder charge or priming com-pound.

Black powder does not cause suffi-cient pressure to generate the high ve-locities associated with modern calibers.Also, the necessity of providing ventsinto the breech to allow ignition of themain charge by the separate primingcompound limited the integrity of the breech relative to maximum sustainablepressures. The metallurgy of the day alsolimited sustainable pressures. Low-pressure black powder charges (under20,000 psi) matched perfectly the sepa-

rately primed, low-pressure weapons ofthe day. Velocities stayed under 2100feet per second (fps). Because separatepriming is unreliable and inconvenient,the search for a better method was a mo-tive factor in firearms development untilthe arrival of "smokeless" powder in thelate 19th Century.

The earliest form of ignition wasnothing more than a lighted match heldin a serpentine lever which, whenpulled, rotated the end of the match untilit came in contact with the flash holeleading into the chamber of the weapon.These early weapons are called match-locks.

In the 16th and 17th Centuries, fire-arms development resulted in weaponscalled wheel locks. The ignition system ofa wheel lock consists of a spring-woundserrated wheel pressed against a piece offlint or steel called a striker. When re-leased by pulling the trigger, the wheelspins against the striker and the resultantshower of sparks ignites the powder. Thesame concept is used in modern day ciga-rette lighters for ignition.

Another development of the 1600'swas the flintlock. This ignition systemconsists of a piece of flint held in the strik-

ing hammer of the weapon. When fired,the hammer would hit a striker plate cov-ering the flash pan containing gunpow-der. As the flint struck the plate, knockingit back from the flash pan, it would sendsparks into the flash pan igniting the gun-powder. The gunpowder would burnthrough the flash hole into the chamber ofthe rifle and ignite the main powdercharge. The flintlock, being far cheaper tomanufacture than the wheel lock, domi-nated firearms design for over two hun-dred years.

Although fulminates of gold and ofmercury had been known since the mid-1600s, they were not considered as prim-ing compounds. These compounds werefar too sensitive and tended to detonate atthe slightest blow or shock.

In 1805, the Reverend John Forsyth ofScotland developed a less sensitive fulmi-nate that he called "Detonating Powder".He announced it as a way to aid shooterstoo long dependent upon flint and steel.Several different methods of using it as apriming compound came about. One of


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the more unusual was the "scent bottle"design.

In this system, the Detonating Pow-der was contained loose in a small bottle

shaped like a perfume bottle. A smallamount was released into the flash panand hit by the hammer. It would deto-nate and set off the main powder charge.All too frequently the scent bottle itselfwould detonate as well. The effect can belikened to a small fragmentation gre-nade.

Another design contained the pow-der in a soft metal tube. When the ham-mer fell, it would shear off a piece of thetube, mashing it under the hammer andsetting it off. This, too, was short lived,as the tube would also occasionally gooff. An American named Guthrie de-signed "pill locks" using the ReverendForsyth's powder. He mixed the powderwith gum, rolled it into small pills andsealed it with wax. Placing one under thehammer primed the weapon.

Numerous attempts followed to en-close the pills in better materials. AFrenchman named Pauly tried papercaps. In 1824, a German named Dreysedeveloped metal caps. But Joshua Shaw,an Englishman who immigrated toAmerica in 1814, developed the first reli-able and convenient system.

Shaw designed a cup shaped con-

tainer to hold a small amount of primingcompound. He covered the compoundwith a piece of foil shellacked in place.The cups fit onto a nipple and, when hit by the hammer, would detonate. The re-sultant flash was directed through thenipple into the chamber, igniting the

main powder charge. Thus was born thepercussion cap firearm.

Initially, Shaw used potassium chlo-rate as the priming compound. Due to its

excessive sensitivity, it was not long lived.He finally standardized on a mixture offulminate of mercury, chlorate of potashand ground glass. The purpose of theground glass was to increase the effect ofthe hammer blow and better insure deto-nation. This composition lasted nearly theentire percussion era.

Shaw's first percussion caps weremade of steel. Next he tried pewter andfinally, in 1816, he used copper. This basicdesign has been in use ever since. Modernpercussion weapons and black powdershooters use percussion caps that areidentical in design to those Shaw createdin 1816. For the first time, a firearms igni-tion system was available that was reli-able, waterproof, and safe. Dozens ofcopies and other claimants followed, butShaw was first.

The next design endeavor was largelydevoted to eliminating separate priming.For every shot with the then existentweapons, the weapon had to be reloadedand reprimed manually. A wide assort-ment of systems was tried, but none sur-passed the simple percussion cap systemdevised by Shaw. Shaw's ideas reignedsupreme in firearms usage until the de-velopment of practical, self contained me-tallic cartridges. Two of the more notablealternative systems were the Lawrencedisk primer and the Maynard tapeprimer.

The Lawrence disk primer used smallcopper disks that contained the priming


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compound. When fired, the systemwould fling one of the disks like a littleFrisbee under the hammer, hopefullytimed so the hammer would hit it. May-nard developed a tape on which pellets

of priming compound were contained.Every time the weapon was cocked themechanism fed the tape under the ham-mer, presenting a new pellet of primingcompound. The same idea can be seentoday in roll caps for children's cap guns.

Other efforts involved inside primingin which the priming compound wascontained inside the cartridge case. In1858 the first successful rimfire car-tridges were developed. Nevertheless,the Civil War (1860-1865) was foughtwith percussion caps. Since the caseheads of inside primed cartridges had to be soft enough to easily indent under the blow of the hammer/firing pin, theywere too weak to contain pressures suffi-cient for effective rifle velocities. How-ever, the Civil War gave considerableimpetus to efforts to develop self-

contained, inside primed cartridges.

From the Civil War period into thelate 1870's, a huge number of primingsystems were created. Of them all, threesurvived the test of time and usage. Onewas the venerable rimfire system nowseen in modern .22-rimfire ammunition.The priming compound is contained in-side the rim of the case. It is detonatedwhen the rim is crushed between the fir-ing pin and the breech face of the barrel.Rimfire cases are not reusable after fir-ing, nor are they suitable for high-pressure loads (20,000 psi or more).

The other two priming systems arecenterfire designs. A centerfire cartridge

holds a separate primer cup in a primer"pocket" in the center of the base of thecartridge. Centerfire cartridge cases arereusable after firing, requiring that thecase be resized to original dimensions, the

spent primer cup be replaced in the base,the powder charge installed and a bulletseated in the case mouth.

The Berdan primer was invented byColonel Hiram Berdan, U.S. Army, atFrankford Arsenal. It consists of an openmetal cup containing the primer com-pound that fits into a "pocket" in the baseof the cartridge case. When struck by thefiring pin, the priming compound iscrushed against an "anvil". The anvil is atripod shaped device. The legs of the an-vil rest against the inside of the pocketand the top of the anvil is directly underthe priming compound. In Berdan prim-ers the anvil is an integral part of the casehead. There are one to three flash holesunder the anvil legs in the case headthrough which the resultant flash can en-ter the case.

In Britain, Colonel Edward Boxer de-veloped a different design. In the Boxerprimer, the priming compound and theanvil are both contained in the primercup. The cup fits into the primer pocket inthe base of the cartridge case. There is onelarge flash hole in the center of the pocket.

Both primers work the same way. Thefiring pin strikes the base of the primercup, mashing the priming compoundagainst the anvil and detonating it. Theresultant flash enters the case through theflash hole and ignites the powder charge.Both primers are equally reliable and nodiscernible difference in accuracy results between the two.


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However, by the late 1880's to early1890's, the U.S. designed Berdan primer became commonly used outside theUnited States, and the British Boxerprimer was standard within the UnitedStates. A possible reason is the ease ofreloading cartridges using the Boxer sys-tem. Reloading ammunition was com-mon among both civilian and militaryshooters. The difficulty and inconven-ience of reloading Berdan primed casesmay have contributed to the decline inusage within the United States.

Priming compound is an explosive

that is detonated by the shock of beingstruck with the firing pin, as opposed tomodern smokeless gunpowder, which isa combustible and generates its energy by burning. Early priming compoundswere composed of various mixtures, cen-tral to which was potassium chlorate.When potassium chlorate oxidizes, itleaves a residue of potassium chloride,which is blown into the pores of themetal. All chloride compounds are hy-droscopic salts that attract and hold wa-ter. Inattentive or incomplete cleaningcan result in a rusted bore literally over-night. These salts are not soluble in oil orsolvents used to clean barrels. They aresoluble in hot, soapy water. The samecleaning procedure using hot, soapy wa-ter is required for black powder residuefor the same reasons.

Fulminate of mercury was also usedin basic priming compounds. It does notleave a corrosive salt-based residue, butthe mercury particles amalgamate withthe brass of the cartridge case and erodeits strength and malleability. Some caseswould be brittle beyond reuse after onlyone firing. The higher the pressures gen-

erated within the cartridge, the faster theeffect. Cartridge case design also has aneffect. Straight walled cases are moreslowly eroded than bottle necked designs.

The advent of modern powders raisedthe need for hotter primer flashes due totheir significantly higher ignition tem-peratures. Hotter temperatures could only be attained by using more priming com-pound, resulting in even more salt andmercuric residue. The development of the bottle necked, high-pressure case finallyeliminated mercury from primer com-pounds.

Mercuric primers were eliminatedfrom U.S. military ammunition about theturn of the century and from U.S. com-mercial ammunition in the 1930's. Someforeign ammunition was still manufac-tured with mercuric primers as recently asthe 1950's. For high-pressure cartridgesand modern smokeless powder, antimonysulfide, lead sulfocyanate and TNT wereadded to the priming mix. These priming

mixtures were used through World WarII.

The first noncorrosive (i.e., free of saltresidue) primers were developed in Ger-many in 1910 in .22-rimfire ammunition.Switzerland followed in 1911. Remingtonintroduced noncorrosive .22-rimfire am-munition in the United States in the1920's. By the 1930's, noncorrosive prim-ers were standard in all commercial am-munition. It wasn't until the 1950's that allmilitary ammunition was made with non-corrosive primers. Today, all ammunition(civilian and military) is noncorrosive andnon-mercuric. Modern primers are builtaround lead styphenate.


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The explosive nature and power ofprimers cannot be overemphasized.Many police departments reload ammu-nition for training and for service use.Primers should be stored in their originalcontainers and handled with care. Aglass jar full of primers can detonate ifdropped on a hard floor with hazardousconsequences.

In fact, all incidents of a cartridge go-ing off when dropped on the ground or"cooking off" when excessively hot arecaused by the sensitive primer com-pound detonating. Modern powder does

not ignite under the shock of beingdropped or hit. Its ignition temperatureis sufficiently high (about 600 degreesFahrenheit) that it will not ignite by itselfunder accumulated ambient heat, suchas occurs when a round is left out in thesun. Of course, when the primer deto-nates it ignites the powder charge. In anunconfined cartridge, the brass case frac-tures like a small fragmentation grenade.Sharp, jagged shards of brass can inflictpainful cuts and be hazardous to theeyes. There is no apparent hazard fromthe bullet itself.

The primer is the first step in thecombustion of gunpowder, which startsthe process of internal ballistics. Origi-nally, the only gunpowder was blackpowder. Black powder is a low orderexplosive. It is a mechanical mixture of

sulfur, carbon (usually charcoal, hencethe name) and saltpeter, which burnswith a great deal of smoke and corrosivesalt residue resulting. Black powder can be detonated by shock.

Modern smokeless gunpowder, onthe other hand, is a combustible, not an

explosive, although it can have an explo-sive effect if burned in confinement. It burns much cleaner than black powder,which is why it was originally known as"smokeless" powder.

Modern smokeless powder is of twotypes. Single based powder is composedof nitrocellulose, a mixture of nitric acidand cellulose such as cotton. Double- based powder is a mixture of nitrocellu-lose and nitroglycerin. All modern pow-ders are either single based or double based powders. They are manufactured inthree different forms - flake powders, ballpowders and extruded powders.

The energy generated by smokelesspowder results from combustion. Thepowder rapidly converts to gas as it burns. The volume of the gas produced ishuge, approximately 4700 times the vol-ume of the powder in its solid state. Whenconfined, as in a cartridge case, the resul-tant pressure propels the bullet down the barrel. Modern cartridges such as the .308

or .223 attain pressures over 50,000pounds per square inch (psi) in millisec-onds.

Modern powders are progressive intheir combustion rates. This means therate of combustion is controlled. Somepowders are fast, some slow. Burning rateis determined by the manufacturers in"closed bomb" tests wherein a small sam-ple of the powder being tested is ignitedin an instrumented container (the"bomb").

Burning rate is relative. In actual use itvaries with cartridge capacity, tempera-ture, humidity, primer flash heat, and ahost of other variables. It is controlled by


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the size of the powder granules, theirshape and chemical retardants added asa coating to the powder. Close examina-tion of extruded and flake powders willreveal small holes through the center of

each granule. These are provided so thegranule will have a constant surface areawhile burning. As the outer surface de-creases, the inner surface of the hole in-creases, keeping the total surface areaconstant.

As the powder burns, the pressuregenerated increases. On a graph, it ap-pears as a rising curve over time to themaximum, or "peak", pressure. Ideally,peak pressure will be attained just priorto the bullet exiting the muzzle. Hencethe need for various burning rates. Theo-retically, the shorter the barrel (or lighterthe bullet), the faster the powder neededfor best efficiency. The ideal barrellength will be just long enough to allowthe peak pressure to form. As the pres-sure rises, it accelerates the bullet tohigher velocities.

Maximum velocity is reached at thepoint just past peak pressure. If the bar-rel is too short, the bullet exits and thepressure dissipates to zero before peakpressure is reached, sacrificing accelera-tion. In a .22 long rifle, peak pressure isreached in about 16 inches of barrel. If a.22 has a barrel longer than 16 inches the bullet is actually retarded by frictionwith the barrel after the moment of peakpressure. However, the loss of velocity isinconsequential in normal barrel lengths.

In a modern centerfire such as the.308, a barrel length of roughly 30-36inches is required to attain completecombustion and peak pressure. A barrel

that length would be unwieldy, heavy,and impractical. So some potential veloc-ity is given up as a practical compromisefor ease of handling and efficiency of rifledesign.

This explains why the .308 (and com-parable high-pressure calibers) has a visible muzzle flash. Since the barrel is tooshort to allow complete combustion of thepowder before the bullet leaves the muz-zle, combustion is completed in the air behind the bullet. The shorter the barrel,the greater the flash if the powder chargeremains the same. The muzzle blast(sound and concussion) is caused by ex-panding gas escaping from the muzzle atsupersonic speeds behind the bullet.

The generation of 50-55,000 psi withinthe rifle is the driving force of internal ballistics. It has numerous effects uponthe cartridge case, the rifle and the bullet,all of which affect the inherent accuracy ofthat rifle and cartridge combination. Noneof these effects can be eliminated. The

manner in which sniper rifles are built isintended to control these effects so thatthey occur in the same way shot aftershot.

Accuracy in a rifle is a direct functionof consistency. Every time a shot is fired,the various parts of the rifle, the cartridgecase and the bullet all move and interactwith each other. The more nearly theseparts move and interact exactly the sameway for each shot, the more accurate thatrifle/cartridge combination will be.

The cartridge case has four functions.First, it acts as the container holding thepowder, bullet and primer. Upon ignitionof the powder charge, the pressure builds


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equally in all directions. To the rear andthe sides, the pressure expands the casewithin the chamber of the rifle forming agas tight seal (the second function). Tothe front, the pressure pushes the bullet

out of the case into the rifling of the boreand down the barrel.

Cartridge cases are made of brass be-cause brass expands easily and uni-formly, and when the pressuredissipates, the brass shrinks enough to be easily extracted. It does not return toits original dimensions, however. If it isto be reused it must be resized to thoseoriginal dimensions. The third functionof the case is to provide proper headspace for the cartridge.

Headspace is a critical internal di-mension. It is defined as the fit of a car-tridge in a chamber measured as thedistance from the face of the bolt to thatpart of the chamber that stops the for-ward movement of the cartridge. Insuffi-cient headspace hinders complete

chambering, and could prevent the boltfrom closing. In effect, the case is toolong for the chamber dimensions. Exces-sive head space can cause case stretchingor separation as the case over expands tofill the chamber, or can cause misfires byallowing the cartridge to move forwardunder the impact of the firing pin, cush-ioning the blow.

Cartridges are designed to headspaceone of four ways: on the case rim (exam-ple: .22 rimfire ammunition); on themouth of the case (example: .45 ACP); onthe shoulder of the case (example: .308)or on a raised belt around the base of thecase (example: 7mm Remington Mag-num).

Cartridges which headspace on theshoulder such as the .308 measure head-space from the face of the bolt to a "datumpoint" located approximately at the mid-point of the shoulder.

To illustrate, when a .308 cartridge isin the chamber of a rifle, it is held by the base against the bolt face and the datumpoint against the corresponding point onthe chamber wall. A .45 ACP roundwould be held by the base of the case atthe back and the mouth of the case at thefront. A .22 rimfire is held by the baseagainst the bolt face and the other side of

the rim held against the back of the breech. In all these cases, the bolt facepushes the cartridge forward until thehead spacing point contacts the interior ofthe chamber and further forward move-ment is stopped.

The final function of the case is to pro-vide uniformity of position within thechamber, both at the base and the neck. Ifthe case head is not square to the face ofthe bolt, the pressures generated willtorque the case within the chamber sincethe part of the base not in contact with the bolt is free to move. One result is that the bullet does not enter the bore concentri-cally. This alone can cause an increase ingroup spread of 0.6 to 2.2 times the aver-age.

A second effect is to create lateral vi-

brations which course down the barrel.These vibrations are due to the bucklingof the action in response to the violent, offcenter push of the cartridge case. Barrelvibrations are discussed more fully be-low.


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The case must hold the bullet in per-fect alignment with the bore of the bar-rel, a condition termed concentricity.Without concentricity, the bullet will en-ter the bore slightly off-center. Thiscauses a deformation of the bullet in the bore. Upon exiting the muzzle, the bulletwill not spin true about its longitudinalaxis, causing the trajectory to vary.Group size will be expanded up to double the average.

Uniformity of the case neck is alsoimportant. If the bullets are not held inthe neck of the case with equal resis-

tance, then the bullets will get faster orslower starts into the rifling. Inconsistentresistance causes the rate of pressure in-crease within the cartridge to vary,which varies the acceleration of the bul-let down the barrel, increasing averagegroup size.

These considerations regarding theeffects of ammunition are resolved byusing the best quality ammunition avail-able. Commercially manufactured matchquality ammunition is readily availablein caliber .308, which is a primary reasonfor the prevalence of .308 sniper rifles.

Match ammunition is manufacturedto higher standards of dimensional uni-formity and component consistency.Without it, no rifle will realize its full ac-curacy potential, regardless of how well

it is built. For example, a rifle that shootsgroups under one half MOA with matchammunition can shoot groups one or twoMOA or larger with general sportingammunition.

The tremendous pressure within thechamber forces the locking lugs of the

bolt back into the lug recesses of the re-ceiver. As with the base of the case, thelocking lugs must be square to the bearingsurfaces of the recesses, and in full, evencontact. Otherwise the pressure is exerted

unevenly and a bending force called"locking lug dispersion" is applied to thereceiver.

Generally, locking lug dispersion willoccur opposite to the plane of the lugs. Ina two lug system (examples: M1 Garand,M14, Mauser and Ruger bolt actions) thedispersion will be greater than in a systememploying three or four lugs. In buildinga sniper rifle, care must be taken to insurethat the locking lugs of the bolt are squareand true within the receiver. Locking lugdispersion is also a source of lateral vibra-tions imposed upon barrel motionthrough the bending of the receiver.

As the powder charge oxidizes and thepressure increases, the bullet begins tomove. The initial resistance of case neckfriction holding the bullet is overcome

and the bullet enters the rifling. The bulletwill enter the rifling more smoothly andwith less distortion if it is allowed to be-gin moving before impact.

If the bullet is in contact with the ri-fling at the start, pressure can build uptoo fast and more randomly as the bulletis forced into the lands of the rifling. Moreconsistent bullet movement and pressureformation is obtained when the bullet hasa small distance to move before impactingthe rifling.

As a rule, the bearing surface of the bullet (that part which contacts the rifling)should be 0.010 inches from the rifling.This is accomplished by limiting the over-


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all length of the cartridge and head spac-ing the rifle to exact dimensions.

For example, the .308 ammunitionused by the FBI is loaded with Sierra

Match 168 grain hollow point boat tail bullets. Overall length is specified at2.800 inches. (Overall length is the lengthof the loaded cartridge from the base tothe tip of the bullet). The chambers of therifles are then hand cut into the barrelsso that the headspace is exactly 1.631inches. The bearing surface of the bulletis then held 0.010 inch from the rifling.

The temperature of high-pressurepowder combustion and the repeatedimpact of bullets into the start of the ri-fling cause barrel throat erosion. Theflash temperature within the chamberexceeds 3500 degrees Fahrenheit. Themelting point of steel is about 2700 de-grees Fahrenheit. The result is that little by little the throat of the barrel where therifling starts is eroded away. The start ofthe rifling is, in effect, moved farther and

farther down the barrel. Eventually, thedistance will be so great that accuracy isdestroyed and velocity is decreased.

The rifling eventually erodes enoughthat the bullet base leaves the case beforethe bearing surface impacts the rifling.The bullet is in free flight within thechamber for a short distance. Accuracy isruined because the bullet is no longerconcentric with the bore. Velocity de-creases as throat erosion progresses dueto the increasing volume of space inwhich the pressure can expand beforemeeting the resistance of the rifling. Thepressure curve is more gradual in itsslope and acceleration is decreased. Tocorrect throat erosion the barrel must be

either replaced or shortened and recham- bered.

The Hornady Manufacturing Com-pany conducted a test with a 7mm Rem-

ington Magnum test barrel that illustratesthe velocity loss due to erosion. Fiverounds were fired and chronographedwhen the barrel was new. Average veloc-ity was 3044 fps. Then 2000 rounds werefired through the barrel after which an-other five rounds were chronographed.Average velocity was 2758 fps.

Hornady Throat Erosion Test

New (fps): 3038 3074 3024 3039 30502000 rds: 2729 2765 2769 2765 2762

The rate of throat erosion and velocityloss will vary with the size of the bore,size of the powder charge being used, rateof fire, and burning rate of the powder.Generally, the smaller the bore and/orlarger the powder charge, the faster therate of erosion. Competitive shooters us-ing large capacity magnum calibers suchas the 7mm Remington or .300 Winchesterwill wash out a barrel throat in 2000rounds or less. The same rifles in .308 canlast 5000-8000 rounds or more.

The bullet impacts the rifling of the bore with considerable force. The bullet islarger in diameter than the bore diameter between the lands of the rifling. It strikesthe rifling sharply before being pressed

into the bore. The effect can be likened tostriking the end of the barrel with a ham-mer. It creates "longitudinal" vibrationswithin the barrel.

At the same time, the rifle is recoilingto the rear in accordance with Newton'sLaw that for every action there is an equal


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but opposite reaction. The direction ofthe recoil force is directly opposite to themovement of the bullet down the barrel,and thus above the point where the buttcontacts the shoulder. The impact of the

bullet into the rifling coupled with theimpact of the stock against the shoulder below the line of recoil force causes therifle to literally buckle in the middle. It bends at the junction of the barrel andthe receiver, and springs back. The resultis an up and down whipping motion ofthe barrel called "vertical" vibrations.

Side to side "lateral" vibrationscaused by any flaws in bedding, incon-sistencies in the shooter's grip or posi-tion, case head or locking lug dispersionwill also be imposed on the barrel. Fi-nally, as the bullet is forced down the bore against the turning of the rifling afourth, spinning vibration is imparted tothe barrel called "torsional" vibration.

These four different vibrations aresimultaneously imposed upon the barrel.

The speed of sound in steel is approxi-mately 17,000 fps. Accordingly, the vibrations reverberate lengthwise withinthe barrel several times before the bulletleaves the muzzle. The resultant motionis barrel whip. Simply stated, the barrelis moving in space about its longitudinalaxis while the bullet is moving the lengthof the bore and exiting the muzzle.

If plotted on an oscilloscope, barrelwhip forms a sine wave pattern. Thehigh points of the pattern are called anti-nodes or overtones. Anti-nodes arewhere the barrel movement is greatest.The intersecting low points are nodes.Nodes are points of little or no move-

ment. It can be likened to whipping a fish-ing rod.

The actual frequency of the barrelwhip will be relatively constant, depend-

ent upon the steel of the barrel, its massand dimensions, the bedding, the bullet,the pressure curve and its magnitude.Barrel whip can be anywhere within a 360degree circumference about the axis of the barrel, but will tend to move predomi-nantly in the vertical plane.

Barrel whip would be an inconsequen-tial consideration if the muzzle of the bar-rel were always a node (a point of little orno motion). If that were the case, the muz-zle would always be at the same point inspace every time a bullet exited. Such auniform "launching site" would be an ac-curate rifle. However, the muzzle is al-ways an anti-node (a point of maximumvibrational motion).

The muzzle has the greatest vibra-tional effect on the direction of the bullet's

flight. The stiffer the barrel, the less theangular displacement of the muzzle. Bar-rel stiffness rises as the cube of barrel di-ameter, and inversely as the square of barrel length. This explains the use oflarge diameter, heavy barrels for accu-racy.

Therefore, in order to be accurate the barrel must always whip with exactly thesame motion from shot to shot in order

for the muzzle to be always at the samepoint in space when the bullet exits. Thisis accomplished in four ways: by usingheavy, large diameter barrels of excep-tionally high manufacturing quality; byusing ammunition of uniform characteris-tics and pressures; by building the rifle in


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such a manner that barrel whip is unim-peded and no extraneous vibrations arecreated; and by shooting the rifle in amanner that does not impair the vibra-tional pattern of the barrel.

First, although manufacturers make barrels in several different ways, the uni-formity of the steel used and the consis-tency of the bore and rifling are theprimary considerations regardless of themanufacturing method used. Custommade barrels are made to more exactingstandards than mass-produced barrels.

For example, Hart Barrel Company ofNew York estimates that of every 100 barrels made, no more than six are per-fect and of the highest possible quality.This means that they will have steel ofuniform density and composition, a boreperfectly straight through the steel andof unvarying diameter throughout, andperfectly cut rifling. Of the remaining 94 barrels, approximately 30-40 will be ofsufficient quality to be sold as lower

grade custom barrels. The remaindersare discarded.

On the other hand, mass produced barrels are manufactured to more liberalstandards. They are intended to providesufficient accuracy to hit a deer at 150yards. Mass producers discard few, ifany, barrels. If not perfectly straight oruniform, the barrel can still be used be-cause the resultant accuracy remainswithin the nominal standards. Barrelscan even be bent until they are straight.General sporting use does not requireminute of angle accuracy, nor does it re-quire the considerable cost of using only best quality barrels.

The vital area on a deer is about 16inches in diameter. To hit a 16-inch targetat normal hunting ranges can be accom-plished quite effectively with a rifle hav-ing a 3 MOA capability. Mass producedweapons and barrels made for generalsporting use shoot 2-3 minutes of angle.This is fine for that purpose, but not forthe law enforcement observer/sniper.

This is not to say that an off-the-shelfrifle is not suitable for sniper utilization.A number of rifles currently availablewould make excellent sniper weaponswith some minimal gunsmithing. The un-

certainty is that they are not individually built to meet accuracy standards neededfor sniper rifles.

There is no way to tell if any onecommercially available rifle has a good barrel except by shooting it. Headspacecan also be excessively generous for ulti-mate accuracy because the manufacturersmust insure the rifle will readily chambera wide variety of commercial and re-loaded ammunition. If the rifle is properly bedded, lugs fitted and it is preciselyheadspaced, failure to attain acceptableaccuracy indicates an imperfect barrel.

Using a less than perfect barrel createsvibrational motion that varies randomly.The muzzle is not at the same point inspace from shot to shot. A mass producedweapon may have a good barrel, or it may

not. The accuracy achieved can varywidely even among rifles of the samemake and model.

A variety of flaws can be present. In-consistent steel composition results in"soft" or "hard" spots in the steel itself.Compositional inconsistencies alter barrel


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vibrations randomly. They also cause the barrel to contort as it heats up throughfiring. Barrels that have been bent tendto revert to their original lines under thestresses of heat and pressure. Flaws in

the bore and rifling result in high or lowspots impeding the progress of the bulletthrough the bore and causing variationsin barrel whip, pressure curve, and bul-let deformation. A custom barrel is ex-pensive, but the necessary quality isguaranteed.

Secondly, the ammunition must beconsistent in its composition, dimensionsand characteristics. Ammunition pro-duced for general sporting use is manu-factured to lower standards than ismatch ammunition. Variations in pres-sure are greater from one cartridge to thenext. This causes wider disparity in ve-locity from shot to shot and wider varia-tions in barrel whip. Any variation in thespeed of the bullet means more or lesstime spent in the barrel. Since the muzzleis constantly moving, such variations

mean that the bullets are not all leavingthe barrel at the same point in space. Avariation of 30 fps between two shots byitself can result in a vertical spread onthe order of one half MOA.

The bullets used in sporting ammuni-tion are not of match quality. Variationsin the bullet composition may be accept-able for sporting use, but they can causean increase in average group size beyondacceptable limits. The importance of the bullet to accuracy is discussed in detail below. (See pages 20-21 and 25-27).

Ammunition is manufactured in uni-form lots. Every lot is assigned its ownunique lot number, which is printed on

the carton case as well as each individual box of ammunition. This is important torecord, since each lot of ammunition isdifferent. When a manufacturer changesany single component, a new lot number

is assigned. The internal capacity of the brass casing will vary from one manufac-turing lot to another. The uniformity ofthe bullets, heat and pressure of the prim-ers, and burning rate of the powder allvary to one degree or another every timethey are changed.

It is not unusual to find one lot ofammunition that shoots extremely well ina particular rifle, and a different lot of thesame ammunition from the same manu-facturer that is not at all accurate in thatrifle. Rifle data records must include thelot of ammunition used. When an accu-rate lot is discovered, it must be reservedfor the rifle that shoots it best. Mixing lotsresults in meaningless accuracy records because uniformity of ammunition is lost.

Third, construction of the rifle affects

the consistency of barrel vibration. Thelocking lugs must be precisely fitted to thelocking lug recesses in the receiver. Thechamber must be precisely headspaced.All the metal parts move and rebound inthe stock with each shot. If this movementis uniform, the metal parts arrive back inthe same relationship with each other andwith the stock after each shot. And theywill react in the same manner from shot toshot while the bullet travels down the barrel.

The receiver and recoil lug are glass bedded to assure uniform movement ofthe action within the stock under recoil.Glass bedding maintains all the majorparts of the rifle in the same exact rela-


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tionship from shot to shot. Also, sinceglass bedding is impervious to moisture,there is no warping pressure on the ac-tion within the stock as occurs withwood stocks which change shape as the

moisture content of the air changes. Theglass bedding must extend forward fromthe receiver for about one inch under the barrel. This "pad" supports the barrel atits junction with the receiver so theweight of the barrel is not hanging onthe threads in the receiver.

From the pad forward, the barrel is"free floated" within the stock. The barrelchannel in the stock is widened so the barrel is clear of any contact with thestock. Any part of the stock in contactwith the barrel will alter barrel whip pat-terns.

Finally, the shooter must insure thatthe rifle is fired in a manner that doesnot impair the vibrational patterns.Nothing can be allowed to contact the barrel. The point of impact can be

changed by merely resting a pencil onthe barrel while firing it. The shooter canalso cause vibrational variations by hold-ing the rifle differently from shot to shot, by shouldering it with varying pressure,gripping it differently or resting the rifleon too hard a surface. For example, if therifle is firmly gripped and tightly shoul-dered for one shot and then held andfired with a relaxed grip and shoulder-ing, a vertical difference of at least 1-2MOA with some lateral dispersion willresult. Understanding these aspects ofthe barrel and its vibrational characteris-tics is vital to accurate shooting.

The last factor of internal ballisticsconcerns the bullet and its movement

through the barrel. The bullet is engravedupon the rifling and is forced to spin as itis accelerated down the barrel. Barrellength and the rate of twist of the riflingwill affect velocity and accuracy. Given

the same powder charge and bullet, thelonger the barrel the higher the velocityuntil the peak pressure is passed, afterwhich the bullet is no longer being accel-erated. As previously stated, a barrel thislong may not be practical and does notcontribute to inherent accuracy.

For example, in the sport of benchrestshooting the goal is to fire five or ten shotsinto as small a group as possible at 100and 200 yards. Benchrest shooters rou-tinely use short, thick barrels of about 20inches in length. The loss of velocity ismore than compensated by the reduced,more uniform barrel whip of the shorter,thicker barrel.

Of greater concern for its affect on ac-curacy is the rate of twist of the rifling,expressed as the length (in inches) of bar-

rel necessary for the rifling to make onecomplete turn. For example, 1 in 12 riflingmakes one complete turn every 12 inchesof barrel and is called a 12-inch twist. Thetwist controls how fast the bullet willspin.

The spin stabilizes the bullet in flightso it will fly nose first. The longer andheavier the bullet in a given caliber, thefaster the twist necessary to stabilize it. Alighter bullet in that same caliber requiresa slower twist to be stable in flight. (Thereason for this is explained below on page21). The velocity of the bullet also affectsthe choice of twist. Increasing velocity in-creases the revolutions per minute (RPM)of the bullet. Optimum accuracy is ob-


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tained by using one bullet weight and barreling with the best twist for that caliber, weight, and velocity combination.Typical RPM for rifle calibers range from150,000 to 200,000. The .308 cartridge

loaded with the Sierra 168 grain HPBT bullet as used by the FBI is best stabi-lized with a 12 inch twist.

The critical feature of the bullet whilewithin the barrel is the base. The base ofthe bullet must form a perfect gas sealcontaining the pressure behind it. The bullet acts like a piston as increasingpressure accelerates it down the barrel. Ifthe base of the bullet is not square, at theinstant the bullet exits the muzzle an un-even push is exerted by the pressure. Ineffect, the bullet is tipped slightly offline. The result is called "axial error", de-fined as an angular displacement of theaxis of rotation. Axial error can also bemechanically induced by nonconcentricammunition, which does not hold the bullet in perfect alignment with the bore.An axial error of 0.001" can result in a

group increase of approximately oneMOA.

This is one reason boat tail bullets are better. It is technologically difficult tomanufacture a flat base bullet with a per-fectly square base. Some bases can sufferdistortion in the manufacturing process,or the lead core may not fully fill the base allowing the pressure during firingto distort the base. In the boat tail design,the "base" is the full diameter circumfer-ence ahead of the stepped down boattail. It is technologically easier to manu-facture a perfect boat tail "base" that issquare to the bullet axis for the pressureto push against. A second reason to use boat tail bullets is the more efficient

aerodynamic design, which is discussedmore fully below. (See pages 26-27).

Axial error can also be induced by adamaged or out of square muzzle, which

allows the high-pressure gas to escapefrom one side of the base sooner or moreforcefully as the bullet exits. For this rea-son, the muzzle of the rifle is recessed sothe bore is countersunk into the end of the barrel. This is called crowning, and isdone to protect the muzzle. This is alsowhy cleaning a rifle must be done fromthe breech end in order to minimize abra-sion or damage to the muzzle.

As long as the bullet is containedwithin the barrel, it rotates about its cen-ter of form. Center of form is the center ofthe shape of the bullet. Once the bulletleaves the barrel, it rotates about its centerof gravity. Center of gravity is the centerof the mass of the bullet. In a bullet, thecenter of form is ALWAYS in front of thecenter of gravity. Thus a bullet is not aform stable projectile. In the air, it would

tumble in flight putting the center of grav-ity in front of the center of form. The spinimparted by the rifling creates gyroscopicstability, which keeps it flying nose first.

By comparison, a dart is a form stableprojectile. The center of gravity of a dart isin front of its center of form, and it willalways fly point first. The greater the dis-tance between a projectile's center of formand its center of gravity, the more unsta- ble the projectile. This explains why, in agiven caliber, a heavier bullet needs afaster twist to stabilize than a lighter bul-let. In a heavier bullet of the same caliber,the center of gravity is moved fartherfrom the center of form as the bullet islengthened for greater weight.


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For optimum accuracy, the center ofgravity must be located exactly on thelongitudinal axis of the bullet. Other-wise, as the bullet is spun down the bar-rel centrifugal force progressivelyincreases from the breech to the muzzle.This can exert considerable force. A 190grain .308 bullet at 2550 fps with the cen-ter of gravity displaced 0.001" creates acentrifugal force at the muzzle of 26foot/pounds. This magnitude of dis-placement can be caused by the bullet jacket being thicker on one side than theother. It can be caused by some fouling,or an imperfection in the barrel "denting"

one side of the bullet.

Regardless, the result is more lead onone side of the longitudinal axis than onthe other, shifting the center of gravity tothe "heavier" side. When the bullet exitsthe muzzle, the centrifugal force createsa sideways "hop" as the bullet, freedfrom the constraints of the barrel, rotatesaround its center of gravity. Instead ofspinning true about the longitudinalaxis, point first through the air, the bulletwill follow a spiraling course about the"true" line of flight and its trajectory willvary tangent to the spiral. A center ofgravity displacement of 0.0005" in a .308match bullet can increase group size ap-proximately one MOA. This is called"radial" error. Axial and radial errorstend to supplement each other.

Mechanical distortions are anothersource of error. No centered bullets, non-concentric ammunition, imperfect throat,or flawed rifling are mechanical distor-tions. They misalign the bullet with thecenterline of the bore, or displace thecenter of gravity by distorting the integ-

rity of the bullet. An error of 0.001" canincrease group size one MOA.

One effect of internal ballistics thatimpacts directly upon the shooter is re-

coil. It starts the moment the firing pinmoves forward. The spring propelling thefiring pin in a rifle will exert a force of 16-30 foot/pounds. The rifle, in accordancewith Newton's law, moves in the oppositedirection. When the firing pin starts for-ward, the rifle starts backward and up-ward. The upward motion is an angle ofmoment caused by the location of thestock below the line of force of the recoil.

The rifle accelerates to the rear as the bullet accelerates down the barrel. Fortu-nately, the acceleration is applied only formilliseconds. If the period of accelerationlasted half a second, the rifle would betraveling rearward at a velocity in excessof 100 miles per hour. The bullet attainsits high velocity in its equally short timeof acceleration because it has a muchsmaller mass and less inertia than the ri-

fle.Recoil effects are produced by the

rearward velocity of the rifle and the re-coil energy that results. It is controlled bya combination of three factors.

Stock design affects the apparent ef-fects of recoil upon the shooter although itdoes not change actual recoil energy at allsince energy is a function of velocity and

mass. However, if a stock design permitsthe point of contact in the shoulder to becloser to the line of bore, the upwardmoment will be reduced. When there isless upward moment, the recoil "seems"less to the shooter, and the rifle is easier tocontrol.


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Increasing the cross sectional area ofthe butt will reduce apparent recoil. Theactual recoil energy remains the same, but spreading it out over a larger buttarea makes it "seem" less.

Since energy is a function of massand velocity, it can be increased or re-duced by altering either variable. De-creasing recoil velocity decreases recoilenergy. That can only be accomplished by decreasing the bullet's velocity, sincethe rifle is merely reacting to the forcesaccelerating the bullet. Lower velocityammunition is not particularly desirable

for the Observer/Sniper. It limits range,decreases penetration and killing power,and increases drop and wind drift.

Increasing the mass of the rifle willdecrease recoil. The increased mass hasincreased inertia, which takes longer forthe acceleration force to overcome. Sinceacceleration continues to be limited induration, the result is lower recoil veloc-ity and energy. The limitation then be-comes one of size and portability.

Generally, a total weight (rifle andscope) between eleven and fourteenpounds will be sufficient to dampen re-coil to controllable levels, yet not be tooheavy or bulky for field use. Some ex-amples are listed below.

Recoil Examples

Caliber Rifle Wt(lbs) Bullet Wt(gr) Velocity(fps) Recoil(ft/lbs)

.223 6.5 55 3200 4.1

.308 11.75 168 2600 11.009

7mm Mag 11.5 168 3000 18.183

300 Mag 11.5 180 3000 21.858

The third means of resolving recoil isthe shooters position and manner of grip-ping the rifle. Holding the rifle with afirm, strong grip and keeping it tightly

against the shoulder will reduce felt re-coil. It will also better insure the recoil isengaged the same way shot after shot,which is conducive to more uniform bar-rel whip and accuracy. A loose grip, orrelaxed position, allows the rifle to recoildifferently from shot to shot. It also in-creases the apparent recoil effects.

If the weapon is firmly shoulderedand gripped, some of the shooters mass isadded to that of the rifle and the resultantrecoil velocity is less. If held 0.25" awayfrom the shoulder and fired, the recoilwould be much worse because the rifle byitself will reach a higher recoil velocity.Accuracy will suffer greatly, as will theshooter's shoulder.

A final factor critical to the accuracyand life of the rifle is proper cleaning.

This is totally within the control of theshooter. Improper or inadequate cleaningwill destroy accuracy and limit barrel lifeto 25-50% of its potential.

With each shot fired, powder residueand bullet fouling is blown into the sur-face of the bore under extreme heat andpressure. The result is that the bore isgradually made smaller and uneven. Thepressure curve is altered, the bullet is de-

formed, barrel whip is randomly altered,and the bore is damaged in the process.Thorough cleaning is the only solution,and it must be done religiously.

As a rule of thumb, one complete pass(in and out) should be made through the bore with a brass brush and solvent for


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every shot fired, but never less than 20complete passes. Even better would be tothen leave the bore wet with solvent for24 hours and repeat the process beforewiping it dry.

The bore should be left dry, not oiled,unless the rifle is to be stored for a pe-riod of months. The bore is sufficientlywork hardened by the passage of the bullets that it will not rust in normal us-age and climatic conditions. If it is oiled,it must be wiped completely dry beforefiring or else the first shot or two will not be on zero.

5. External BallisticsExternal ballistics is the science of the

bullet in flight. It involves everythingthat occurs from the instant the bulletleaves the muzzle until it impacts its tar-get. An understanding of the factors andeffects of external ballistics is imperative.Sound marksmanship, experience, and asolid understanding of those factors andeffects will enable the Observer/Sniperto compensate and hit the intended tar-get.

Two forces influence the bullet inflight. One is gravity, which is constant.The other is air resistance; more com-monly called "drag". Of the two, gravityhas the least effect. If a .30/06 bulletwere fired in a gravity free atmosphere,it would travel slightly less than two

miles and stop in midair.That same bullet, fired in a vacuum

but with gravity present, would travelabout 43 miles and strike the earth at thesame velocity it left the muzzle. In theworld of reality where both forces exist,

gravity pulls the bullet down while dragsimultaneously slows the bullet.

Gravity is a constant acceleration ofthe bullet downwards at the rate of 32 feet

per second, per second. A simplified ex-ample is that after one second, a fallingobject has a velocity of 32 fps. After twoseconds, its velocity is 64 fps, and so on. Itacts independently of the bullet's weight,shape or velocity. The instant a bullet ex-its the muzzle, gravity accelerates it downat the constant rate of 32 fps/ps.

Theoretically, if a bullet were droppedfrom beside the muzzle at the exact in-stant an identical bullet was shot from themuzzle, they would both hit the groundat the same time, albeit widely spreadapart. This is true in a vacuum. In actual-ity, the fired bullet lands slightly after thedropped bullet because it generates somelift as it flies through the air. The lift coun-teracts gravity to a small degree.

The longer the time of flight, the faster

the bullet's falling velocity becomes, untilit reaches a terminal velocity on the orderof 250 fps. "Terminal velocity" is that ve-locity at which drag has increased to thepoint gravitational acceleration is coun-teracted. Bullets do not have a time offlight long enough to reach terminal ve-locity as they drop. A typical .308 roundtakes approximately one tenth of a secondto travel two hundred yards.

Drag works in opposition to the direc-tion of velocity. Although all objects fall atthe same rate regardless of shape, size, orweight, they do not all reach the sameterminal velocity because drag varies withshape, weight, and surface area. Thus afeather and a rock do not hit the ground


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at the same time when dropped simulta-neously, although they would if droppedin a vacuum.

Gravity gives the bullet's line of

flight, called the "trajectory", its curvingshape. The trajectory of a bullet is a"parabolic curve", which is defined as aconstantly increasing curve. The slope ofthe curve becomes steeper as range in-creases. The distance a bullet is belowthe line of bore is called "drop". Since thetrajectory is a parabolic curve, the dropincreases with range. For example, at themuzzle drop is zero. At 100 yards, thedrop of a typical .308 flat base bullet is2.56 inches. At 200 yards, the drop is11.09 inches, and at 1000 yards it is478.28 inches.

In order to hit a target, the line of bore, as represented by the barrel, must be angled up relative to the horizontal.This angle is called the "angle of depar-ture". The result is that the bullet crossesthe shooter's line of sight twice.

Line of sight is a straight line throughthe sights to the target, and is above the barrel. The bullet crosses it once close tothe muzzle on the way up, and again atsome point down range on the waydown. With scoped rifles the line of sightis typically 1.5 inches above the muzzle,and the bullet first crosses it at a range between 22 and 25 yards.

The second intersection with the lineof sight is the zero point of the rifle. Thezero point is altered by raising or lower-ing one of the sights until it coincideswith the desired zero for the weapon.Raising or lowering the sight changes theangle of departure, moving the zero

point closer or farther away. The actualdimensions involved are very small, yettheir effects are monumental. For exam-ple, to be zeroed at 1000 yards, the angleof departure for a typical .308 match bul-

let will be on the order of 3 degrees. Thisalso accentuates the large effects of thesmall errors discussed in the sectionabove on Internal Ballistics.

Velocity is the only factor that influ-ences the perceived effects of gravity, andthen only relative to a specific range.Gravity acts on the bullet only for the du-ration of its horizontal flight vector. Thefaster a bullet arrives at the target, the lesstime gravity has to pull it down. The re-sult is less drop and a flatter trajectory. Asan example, if a bullet takes one second toreach its target it will drop 32 feet. Afaster bullet reaching the same target inone half second will drop 16 feet. Thefaster bullet will require less sight ad- justment, and will travel closer to the lineof sight between the muzzle and the tar-get.

The second force that influences the bullets flight is drag. Drag resists veloc-ity, increasing exponentially as velocityincreases. The higher the velocity, thegreater the drag and the greater the rate atwhich velocity is lost.

As an example, a 180 grain .308 flat base bullet with a muzzle velocity of 2100fps will have a retained velocity at 1000yards of 1045 fps - a loss of about 50 per-cent. That same bullet with a muzzle ve-locity of 3200 fps will have a retainedvelocity at 1000 yards of 1433 fps - a lossof 55 percent. The faster bullet has ahigher rate of velocity loss. It has a greaterretained velocity because it had a greaterinitial velocity. This illustrates the in-


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crease of drag with an increase of veloc-ity. It also affects the trajectory since thetime of flight increases as the velocitydecays, thereby giving gravity more timeto act upon the bullet.

Drag represents energy given up bythe bullet pushing the air aside as it flies.The air is compressed by the nose of the bullet and forced out of the way. As theair stream moves down the sides of the bullet, friction with the sides causes turbulence. The turbulence "drags" againstthe bullet, another component of the re-tarding effect of drag. As the air spills offthe rear of the bullet, more turbulence iscreated along with a partial vacuum atthe base, both of which act to furtherslow the bullet. Bullet shape and designare the important factors relative to drag.

Bullets are designed for various pur-poses. A particular purpose may not beconducive to an aerodynamically effi-cient design. For example, ammunitionintended for use in tubular magazines is

loaded with flat nosed or round nosed bullets to prevent accidental dischargesin the magazine when recoil bangs thenose of the bullet against the primer ofthe round ahead of it. Flat nosed orround nosed designs are not aerody-namically efficient. A sharp pointed bul-let would be far more efficient relative todrag, but not at all useful in a tubularmagazine.

The aerodynamic efficiency of a bul-let is expressed as "ballistic coefficient".Ballistic coefficient is a three-digit number less than one, which denotes the bul-lets ability to overcome drag. The higherthe number, the more efficient the bullet.A ballistic coefficient of 1.000 would rep-

resent a bullet that did not lose any veloc-ity to drag, an impossibility.

According to the Sierra Bullet Manu-facturing Company, their 180 grain .308

round nosed bullet has a ballistic coeffi-cient of 0.250. The Sierra 180 grain .308hollow point boat tail match bullet has a ballistic coefficient of 0.538. As would beexpected, the hollow point boat tail bulletis far more aerodynamically efficient thanits round nosed counterpart. To illustratethis, assume each bullet is started with amuzzle velocity of 2600 fps. At 500 yards,the round nosed bullet has a retained ve-locity of 1296 fps - a loss of 50 percent.The boat tail bullet has a retained velocityof 1853 fps - a loss of 29 percent. Thehigher velocity of the boat tail bullettranslates into a flatter trajectory and de-creased wind deflection. It also meansmore energy delivered on target. Theseare all vital considerations for the Ob-server/Sniper selecting a bullet for use.

.308 180grBullet B.C. MV 100 200 300 500

RN .250 2600 2271 1967 1702 1296

Bullet Path: -1.5 2.64 0.0 -11.66 -74.96

HPBT .538 2600 2439 2284 2134 1853

Bullet Path: -1.5 2.17 0.0 -8.82 -50.48

Ballistic coefficient is independent of bullet weight and caliber in its effect, al-though increasing weight in a specificcaliber will increase ballistic coefficient.The ballistic coefficient for a 150-grainround nosed .308 is 0.213, and for a 180grain round nosed .308 it is 0.267. If two bullets have the same ballistic coefficient,and the same muzzle velocity, they will


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have identical trajectories regardless oftheir caliber, shape, or weight. Sierras.224 caliber 45 grain spitzer with a ballis-tic coefficient of 0.213 and the abovecited 150 grain .308 round nosed bullet

will have the exact same trajectories,given the same muzzle velocity.

Small differences in ballistic coeffi-cient have relatively insignificant effect,especially at ranges under 500 yards. Forexample, if the .308 caliber Sierra 168grain HPBT (ballistic coefficient 0.475)and the .375 caliber Sierra 300 grain softpoint boat tail (ballistic coefficient 0.493)are both started at 2600 fps, they willhave essentially the same trajectory outto 500 yards.

Comparison of Similar Coefficients

300gr .375 SPBT v. 168gr .308 HPBT

Muzzle Velocity: 2600 fps

Bullet BC 100 200 300 500 1000

300sp .493 2449 2304 2163 1897 1329

Bullet Path: 2.14 0.0 -8.67 -49.28 -349.6

168hp .475 2417 2241 2073 1758 1145

Bullet Path: 2.22 0.0 -9.13 -53.06 -407.1

Bullets suitable for the Observer/Sniper are of two basic designs. One isthe traditional flat base design, the otherthe boat tail design. Of the two, the boattail is far superior. As discussed in thesection on Internal Ballistics above, a

boat tail bullet has a more uniform basethan a flat base design.

Secondly, boat tail bullets are moreaerodynamically efficient. They createless drag in their flight. The air streamspills off the tapered rear of the bulletmore smoothly, creating less turbulence

and less of a vacuum. That equates to lessdrag. A small hollow point will reducethe compaction of air at the nose and theresultant turbulence. It acts like a smallcookie cutter against the denser, com-

pacted air. The shock waves that arecaused by the bullet's passage are morestreamlined. In actuality, the improve-ment in aerodynamic performance is notsignificantly greater than that of equalquality flat base bullets except at extremerange, but it is better. Lastly, boat tail bul-lets are less damaging to the barrel of arifle.

Frankford Arsenal ran an extensivetest of the effects of bullet design on bar-rel life. Their tests determined that usingflat base bullets improved the accuracy ofa barrel for the first 2000 rounds. The ac-curacy leveled off up to about 5000rounds. After 5000 rounds accuracy felloff as the barrel deteriorated. With boattail bullets, accuracy improved dramati-cally the first 300-500 rounds. It continuedto improve up through 3000 rounds.

Through 8000 rounds accuracy showedminor but continuing improvement beforeleveling off. The barrels did not begin todeteriorate until about 10,000 roundswere fired. The exclusive use of boat tail bullets coupled with proper cleaning candouble the effective life of the barrel.

Once the trajectory is understood, therifle can be fired accurately. Knowing thetrajectory allows the shooter to know ei-ther where to aim or how to adjust thesights in order to hit a precise target. Forexample, the FBI uses .308 ammunitionloaded with Sierra 168 grain hollow point boat tail (HPBT) bullets to a muzzle veloc-ity of 2650 fps at standard tempera-ture/pressure. (Standard temperature and


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pressure is 59 degrees Fahrenheit at sealevel, or 29.92 inches of mercury). The bullet has a ballistic coefficient of 0.475.Specifying the temperature and air pres-sure is important because the velocity

and trajectory will vary. Most published ballistic tables and trajectory data arelisted for standard tempera-ture/pressure.

When zeroed at 200 yards, the bulletis never more than 2.1" above the line ofsight from the muzzle to the zero range.The zero range is where the point of aimand the point of impact coincide - 200yards in this example. At 250 yards, the bullet is 3.5" low. At 300 yards, it is 8.8"low. The Observer/Sniper will knowthat with this zero, he must aim 3.5" highto hit his point of aim at 250 yards, andalmost nine inches high to hit at 300yards.

Knowing the trajectory of the bullet ishalf the problem facing the Ob-server/Sniper. The range must also be

known, or accurately estimated, for pre-cise shooting. There are a number ofmethods for estimating range. An ex-perienced Observer/Sniper will use acombination of them.

These methods are: actual distancemeasurements using range measuringdevices, maps, blueprints, estimation byeye, comparison with known dimen-sions, and the use of the scope reticle.The reticle of the scope can be an excel-lent range finding device, about whichmore is discussed below. (See pages 41-42). Most commercially available rangefinders sold for sporting use have toogreat a margin of error to be effective.The readings can be off by plus or minus

10-20%. On the other hand, currentlyavailable laser range finders are ex-tremely accurate, to plus or minus onehalf of one percent, and are small, conven-ient, and expensive.

Actually measuring distances is apractical preparatory step to take in loca-tions where Observer/Sniper utilizationcan be anticipated, such as airports andaround government buildings. Anotherpreparatory step is to measure the dis-tance of various common dimensions,such as the spacing of electric poles, thelength of street blocks, the width ofstreets, etc. Knowing these common di-mensions allows the Observer/Sniper toestimate range by comparing the locationof the target with known common dimen-sions in between the Observer/Sniper andthe target. Many locations are accuratelymapped, and these maps can provide de-tailed range data for the Observer/Sniper.Again, airports are a prime example.

Estimation by eye is a matter of ex-

perience, practice, and learning the ap-pearance of common objects at variousranges. Estimation by eye can be severelyinfluenced by the nature of the terrain, thelight and atmospheric conditions, and theamount of the target visible.

Looking across a hidden depression,downward from high ground or along astraight open road will make objects ap-pear closer than they are. Looking acrossa visible depression, looking upwardfrom low ground or when the field of vi-sion is narrowly confined as in foresttrails or crooked streets will make objectsappear farther than they are. Objects willappear closer when clearly seen and out-lined, or when seen over uniform surfaces


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like snow or water, or when the sun is behind the observer. They will seem far-ther away when obscured or small in re-lation to the surroundings, when they blend into the background, when seen in

poor light such as dusk or dawn, whenseen in the rain, snow or fog, or whenthe sun is in the observer's eyes. Estima-tion by eye should never be used as thesole means of estimating range except asa last resort.

Proper zeroing of the rifle can sim-plify the range estimation problemgreatly. Refer again to the example citedabove using the Sierra 168 grain HPBTzeroed at 200 yards. Since the bullet isnever more than 2.1" from the line ofsight to about 225 yards, in practice theObserver/Sniper can take headshots outto 225 yards merely by holding center.This virtually eliminates the problem ofrange estimation at practical law en-forcement ranges. In effect, the Ob-server/Sniper with a 200 yard zero has a"point blank" range of approximately 225

yards.

Point blank range is that distancewithin which the shooter need not esti-mate range. The bullet is close enough tothe line of sight that the shooter for allpractical purposes can consider the pointof aim and the point of impact to coin-cide.

fbi advanced rifle training for the observer sniper

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