The more energy is transferred, the greater the wound in the target and the more likely it is to stop that target. The lead core in normal “ball” ammunition expands upon impact, which increases the diameter of the projectile and aids in transferring energy from the moving projectile to the target. Some of the most recent studies indicate that with a common 16″ barrel in an AR carbine, M855 ammo has severely degraded performance past 150 yards and is only effective to about 500 meters (versus the 600 meters at which it was designed to penetrate a steel helmet with a standard M-16).Īnother issue was the lack of expansion. The 5.56 NATO cartridge is highly dependent on velocity to generate the energy it transfers to targets, and lower velocity means a much lower muzzle energy. As the barrel length of commonly used firearms continued to decrease, the velocity of the round when it exited the barrel decreased as well. There were still some major issues, though. The solid-steel penetrator added much needed stability to the projectile when traveling through barriers since there was no longer any soft lead to deform upon impact, and increased the stability and accuracy of the round when traveling over long distances due to the increased mass of the projectile. The internal construction of M855 green-tip ammo differs from the standard “ball” M193 cartridge in one very important way: there’s a steel core at the tip of the projectile. While the military did adopt a 77-grain lead projectile for long range shooting, they developed the M855 projectile specifically for hitting targets behind light barriers (like glass and tin and heavy clothing). Soldiers in the field reported issues with the projectile when it penetrated glass or other intermediate barriers, and wanted a heavier projectile to aid in energy transfer to targets downrange (putting down enemy soldiers more efficiently). Even with the lighter projectile, that “armor piercing” capability was still maintained throughout the design process.Īfter the Vietnam war, there were some deficiencies that needed to be addressed. That faster-fps yet lighter bullet meant that the cartridges were lighter, and therefore the soldier on the field could carry more ammunition into battle than ever before. Increased velocity meant increased muzzle energy, and provided the power to meet the specifications. The original mil-spec parameters for the M-16 rifle were that it needed to penetrate the steel helmet of an enemy soldier at a given distance, and while the lighter overall weight of the projectile reduced the penetration power of the projectile at long distance, the designers of the ammunition compensated with increased muzzle velocity. The 55-grain FMJ projectile was of the same construction that had been used in similar projectiles for close to a century, namely a solid lead core surrounded by a copper jacket. military, the ammunition that accompanied it was designated the M193 cartridge - a standard brass case “ball” full-metal-jacket (FMJ) 5.56 round. When the M-16 was first fielded by the U.S.
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