Armor-piercing bullets forrifle andhandguncartridges are designed to penetrateballistic armor andprotective shields intended to stop or deflect conventionalbullets. Although bullet design is an important factor with regard to armor penetration, the ability of any givenprojectile to penetrate ballistic armor increases with increasing velocity. Rifle cartridges typically discharge bullets at highermuzzle velocity than handgun cartridges due to largerpropellant charge. However, even the same cartridge (one that is interchangeable between specific rifles and handguns) fired from a rifle will, in almost all common cases, have a higher velocity than when fired from a handgun. This is due to the longer period of acceleration available within the longergun barrel of rifles, which allow adequate time for the propellant to fully ignite before the projectile exits the barrel. For this reason, bullets fired from rifles may be more capable of piercing armor than similar or identical bullets fired from handguns.[1] In addition, a small-caliber bullet has highersectional density than a larger-caliber bullet of the same weight, and thus is more capable of defeating body armor.
Armor-piercing bullets typically contain ahardened steel,tungsten, ortungsten carbide penetrator encased within acopper orcupronickel jacket, similar to the jacket which would surroundlead in aconventional projectile. The penetrator is a pointed mass of high-density material designed to retain its shape and carry the maximum possible amount of energy as deeply as possible into the target. The entire projectile is not normally made of the same material as the penetrator because the hard metals of good penetrators would damage the barrel of the gun firing the bullet. Impact velocity of the copper jacket may temporarily soften the face of the armor and cushion the impact to avoid breaking the brittle penetrator. The penetrator then slides out of the jacket to continue forward through the armor.[1]
| Round | Projectile | Weight (grains) |
|---|---|---|
| M2 | .30-06 Springfield | 163 |
| M61 | 7.62×51mm NATO | 150.5[2] |
| SS190 | FN 5.7×28mm | 31 |
| M995 | 5.56×45mm NATO | 52[2] |
| M993 | 7.62×51mm NATO | 126.6 |
| 7N13 | 7.62×54mmR | 145.1 |
| S.m.K. | 7.92×57mm Mauser | 178.25 |
| AP485 | .338 Lapua Magnum | 248[3] |
| 211 Mod 0 | .50 BMG | 650 |
Handgun bullets made entirely of lead have less penetration ability than jacketed bullets at similar velocity. In the 1930s,Western Cartridge Company introduced.38 Special ammunition capable of firing a 158-grain (10.2 g) copper-tipped lead-alloy bullet at 1,125 feet (343 m) per second to penetrate sheet-metal automobile doors.[4] As higher velocity handgun cartridges became available and jacketed bullets became more common in handgun cartridges, armor penetration was improved with thicker bullet jackets or bullets made entirely of jacket material like copper orbrass. Later designs used penetrator cores similar to rifle designs.[1] Some of these bullets werecoated with Teflon to reduce their tendency toricochet off glass or sheet metal.[5]
In 1986 United States law initially defined armor-piercing bullets to exempt rifle ammunition:
Subsequent regulations requiringgreen bullets encouraged replacing lead core bullets with M855A1 military bullets with a copper jacket over a steel core,[7] or hunting bullets of solid copper or brass.[8]