Terminal ballistics Terminal ballistics, a sub-field of ballistics, is the study of the behavior and effects of a projectile when it hits its target.[1] Terminal ballistics is relevant both for small caliber pro- jectiles as well as for large caliber projectiles (fired from artillery). The study of extremely high velocity impacts is still very new and is as yet mostly applied to spacecraft design. 1 General An early result is due to Newton; the impact depth of any .32 ACP full metal jacket, .32 S&W Long wadcutter, .380 ACP projectile is the depth that a projectile will reach before jacketed hollow point stopping in a medium; in Newtonian mechanics, a pro- jectile stops when it has transferred its momentum to an equal mass of the medium. If the impactor and medium 2.1.1 Target shooting have similar density this happens at an impact depth equal to the length of the impactor. For short range target shooting on ranges up to 50 me- For this simple result to be valid, the arresting medium is ters (55 yd), aerodynamics is relatively unimportant and considered to have no integral shear strength. Note that velocities are low. As long as the bullet is balanced so it even though the projectile has stopped, the momentum is does not tumble, the aerodynamics are unimportant. For still transferred, and in the real world spalling and similar shooting at paper targets, the best bullet is one that will effects can occur. punch a perfect hole through the target. These bullets are called wadcutters. They have a very flat front, often with a relatively sharp edge along the perimeter. The flat front punches out a large hole in the paper, close to, if not equal 2 Firearm projectiles to, the full diameter of the bullet. This allows for easy, unambiguous scoring of the tar- 2.1 Classes of bullet get. Since cutting the edge of a target ring will result in scoring the higher score, fractions of an inch are impor- tant. Magazine-fed pistols may not reliably feed wadcut- There are three basic classes of bullet: ters because of the angular shape. To address this, the semiwadcutter is used. The semiwadcutter consists of a • those designed for maximum accuracy at varying conical section that comes to a smaller flat, and a thin ranges sharp shoulder at the base of the cone. The flat point punches a clean hole, and the shoulder opens the hole up cleanly. For steel targets, the concern is to provide • those designed to maximize damage to a target by enough force to knock over the target while minimizing penetrating as deeply as possible the damage to the target. A soft lead bullet, or a jacketed hollow-point bullet or soft-point bullet will flatten out on • those designed to avoid over-penetration of a target, impact (if the velocity at impact is sufficient to make it by deforming to control the depth to which the bullet deform), spreading the impact over a larger area of the penetrates, which as a by-product, deals more dam- target, allowing more total force to be applied without age inside the wound. damaging the steel target. There are also specialized bullets designed for use in long The third class may limit penetration by expanding or range precision target shooting with high-powered ri- fragmenting. fles; the designs vary somewhat from manufacturer to 1 2 2 FIREARM PROJECTILES manufacturer, but all are based on the MatchKing bullets customized rifle with an appropriately cut chamber and a introduced by the Sierra Bullet Company around 1963. fast-twist bore. Based on research done in the 1950s by the U.S. Air Force, in which it was discovered that bullets are more stable in flight for longer distances and more resistant to 2.1.2 Maximum penetration crosswinds if the center of gravity is somewhat to the rear of the center of pressure, the MatchKing bullet (which is For use against armored targets, or large, tough game an- still in wide use and holds many records) is a hollow point imals, penetration is the most important consideration. design with a tiny aperture in the jacket at the point of the Focusing the largest amount of momentum on the small- bullet and a hollow air space under the point of the bullet, est possible area of the target provides the greatest pen- where previous conventional bullets had had a lead core etration. Bullets for maximum penetration are designed that went all the way up to the point.[2] to resist deformation on impact, and usually are made of lead that is covered in a copper, brass, or mild steel jacket Other designs from other manufacturers may be anything (some are even solid copper or bronze alloy). The jacket from close copies of the MatchKing design to hollow completely covers the front of the bullet, although often point bullets with a deep, wide cavity containing a long, the rear is left with exposed lead (this is a manufacturing slender, pointed plastic or aluminum plug. In all these consideration: the jacket is formed first, and the lead is cases, the bullet is designed to have its center of gravity swaged in from the rear). to the rear of its center of pressure. MatchKing-type hol- low point bullets, as contrasted with hollow point bullets For penetrating substances significantly harder than jack- intended for hunting or police use, are not designed to eted lead, the lead core is supplemented with or replaced flatten out on impact; this makes them a relatively poor with a harder material, such as hardened steel. Military choice for hunting, as they tend to perform erratically armor piercing small arms ammunition is made from a and unpredictably upon entering an animal’s body—they copper-jacketed steel core; the steel resists deformation may tumble, or break apart, though most often they punch better than the usual soft lead core leading to greater pen- straight through making a narrow wound that usually does etration. The current NATO 5.56mm SS109 (M855) bul- not cause death quickly. The U.S. military now issues let uses a steel tipped lead core to improve penetration, ammunition to snipers that use bullets of this type. In the steel tip providing resistance to deformation for armor 7.62×51mm NATO, M852 Match and M118LR ammu- piercing, and the heavier lead core (25% heavier than the nition are issued, both of which use Sierra MatchKing previous bullet, the M193) providing increased sectional bullets; in 5.56×45mm NATO, those U.S. Navy and U.S. density for better penetration in soft targets. For larger, Marine snipers who use accurized M16-type rifles are is- higher velocity calibers, such as tank guns, hardness is of sued the Mk 262 Mod 0 cartridge developed jointly by secondary importance to density, and are normally sub- Black Hills Ammunition and Crane Naval Surface War- caliber projectiles made from tungsten carbide, tungsten fare Center, using a bullet manufactured by Sierra Bullets hard alloy or depleted uranium fired in a light aluminum that was cannelured according to military specifications or magnesium alloy (or carbon fibre in some cases) sabot. for this project. Many modern tank guns are smoothbore, not rifled be- In 1990, the U.S. Army Adjutant General’s Office issued cause practical rifling twists can only stabilize projectiles, a legal opinion holding that the Sierra MatchKing bullet, such as an armour-piercing fin-stabilized discarding sabot despite being an open-tip design, is not designed specif- (APFSDS), with a length to diameter ratio of up to about ically to cause greater damage or suffering in a human 5:1, the spin imposed by rifling interferes with shaped target, and in fact normally does not create a wound read- charge rounds, and also because the rifling adds friction ily distinguishable from wounds caused by conventional and reduces the velocity it is possible to achieve. To get full metal jacket bullets, and is therefore in their opinion the maximum force on the smallest area, anti-tank rounds legal under the Hague Convention for use in war.[3] have aspect ratios of 10:1 or more. Since these cannot be stabilized by rifling, they are built instead like large darts, For ultra long range precision target shooting with with fins providing the stabilizing force, negating the need high-powered rifles and military sniping, radically de- for rifling. These subcaliber rounds are held in place in signed very-low-drag (VLD) bullets are available that are the bore by sabots. The sabot is a light material that trans- generally produced out of rods of mono-metal alloys on fers the pressure of the charge to the penetrator, then is CNC lathes. The driving force behind these projectiles discarded when the round leaves the barrel. is the wish to enhance the practical maximum effective range beyond normal standards. To achieve this, the bul- lets have to be very long and normal cartridge overall 2.1.3 Controlled penetration lengths often have to be exceeded. Common rifling twist rates also often have to be tightened to stabilize very long The final category of bullets is that intended to control projectiles. Such commercially nonexistent cartridges penetration so as not to harm anything behind the target. are termed “wildcats”. The use of a wildcat based (ul- Such bullets are used primarily for hunting and civilian tra) long-range cartridge demands the use of a custom or antipersonnel use; they are not generally used by the mil- 2.1 Classes of bullet 3 itary, since the use of expanding bullets in international to expand the damaged area.