Wounding Effects of the U.S. Military M193 (M16A1) and M855 (M16A2) Bullet Cartridges
Exaggerated descriptions of the wounding effects of the M16 rifle bullet flourish as great works of urban lore. One fable describes a bullet that tumbles end-over-end in flight as soon as it exits the muzzle of the rifle. Another legend provides a dramatic account of an unstable, super-high velocity bullet that tumbles and chews its way through flesh like a buzz saw. Although there appears to be a tinge of half-truth behind these entertaining and awe-inspiring mythical tales, these stories do not represent an accurate description of the wounding characteristics of the M16 bullet.
When the M16 cartridge is fired and the bullet is propelled down the bore, the bore’s rifling imparts a gyroscopic spin to the bullet. This gyroscopic rotation is needed to maintain point forward stabilization of the bullet as it flies through the air. This method of bullet stabilization is identical to the rotational spin applied to a football when thrown by a quarterback (American football).
The Earth’s gaseous atmosphere is approximately 400 times less dense than the body's soft tissues. When the M16 bullet strikes and plows into the body, the rotational spin that stabilized its flight through the air is insufficient to maintain its stability as it flies through dense tissue. The bullet typically penetrates point forward for approximately 4-5 inches before it begins to seek a state of stability in the body.
The bullet’s pointed shape makes it heavier at its base than its nose, producing a center of gravity that is located aft of its longitudinal centerline. When the bullet hits the body and penetrates, the bullet attempts to rotate 180 degrees around its center of gravity to achieve a base forward orientation. This backwards orientation is the bullet’s stable position in tissue because it places the center of gravity forward.
As the bullet yaws through 90 degrees and is traveling sideways through flesh, the stress of tissue resistance to bullet passage can overpower the physical integrity of the bullet. The bullet has a groove around its midsection called a cannelure. The purpose of the cannelure is to permit the mouth of the cartridge case to be crimped tightly against the bullet shank to hold it firmly to the case. The cannelure weakens the structural integrity of the bullet's copper jacket.
At distances of 100 yards and under, when the bullet hits the body and yaws through 90 degrees, the stresses on the bullet cause the leading edge to flatten, extruding lead core out the open base, just before it breaks apart at the cannelure. The portion of the bullet forward of the cannelure, the nose, usually remains in one piece and retains about 60 percent of the bullet's original weight. The portion of the bullet aft of the cannelure, the base, violently disintegrates into multiple lead core and copper jacket fragments, which penetrate up to 3-inches radially outward from the wound track. The fragments perforate and weaken the surrounding tissues allowing the subsequent temporary cavity to forcibly stretch and rip open the multiple small wound tracks produced by the fragments. The resulting wound is similar to one produced by a commercial expanding bullet used for varmint hunting, however the maximum tissue damage produced by the military bullet is located at a greater penetration depth.
(The increased wounding effects produced by bullet fragmentation were not well understood until the mid-1980’s. Therefore the wounding effects of the original M16 rifle bullet were not an intentional U.S. military design characteristic.)
At distances between 100-200 yards the bullet commonly breaks in half at the cannelure forming two large penetrating fragments, the nose and base.
At distances beyond 200 yards the bullet usually remains intact due to velocity decay. It simply yaws 180 degrees to penetrate backwards through the body.
Both the M193 and M855 bullets demonstrate similar terminal performance as described above, when fired from rifles fitted with a 20-inch or longer barrel.
Shooting the M193 or M855 from a rifle with a barrel length less than 14.5-inches produces insufficient muzzle velocity to achieve the terminal performance described above. A rifle fitted with a 14.5-inch barrel is adequate for close-quarters battle. For engagements anticipated at greater than room distance but less than 100 yards, a rifle fitted with a 16.5-inch barrel should be employed to ensure sufficient velocity.
The older 55-grain M193 (M16A1) cartridge is not sensitive to rifling twist rate and can be fired in rifles with 1:12, 1:9 and 1:7 rates of twist. However, the newer M855 (M16A2) cartridge is best used with a rifling twist rate of 1:7 or 1:9. When the M855 is fired in a rifle with a slower rate of twist the longer 62-grain bullet can yaw up to 70 degrees in free trajectory through the air, substantially degrading accuracy.
The wound ballistics of the U.S. military Olin M193/Winchester 55 grain FMJ (X223R1 or Q3131) and green tip U.S. military Olin M855/Winchester 62 grain FMJ (RA556M855) cartridges makes them an adequate choice for use against violent criminal offenders.
Additional testing has indicated that errant bullets (military FMJ and commercial .223 Remington JSP/JHP) which do not hit an attacker appear to penetrate fewer walls and other common building materials than stray handgun bullets.
Originally Posted by skinnadoor
Cogito ergo armatus sum
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