the M855 bullet's performance falls off sharply beyond 300 meters. The ranges are even shorter for short-barreled carbines. Half of small-arms attacks were launched from 300 to 900 meter ranges. An M855 fired from an M4 Carbine has severely degraded performance beyond 150 meters. The maximum effective point target range of an M4 carbine with M855 rounds is , with a maximum effective area target range of . These mark the greatest distances the rounds can be expected to accurately hit the target, not the ranges that they have terminal effectiveness against them. Because the M855 is yaw dependent it requires instability in flight to deform upon hitting the target. It is the most stable in flight between , potentially lessening its effectiveness if it strikes an enemy between those distances. In addition to this, tests have shown that 5.56 mm bullets fragment most reliably when traveling faster than . From full-length rifle and machine gun barrels, rounds exhibit velocities above out to . An M855 fired from a shorter barreled M4 carbine exhibits a bullet velocity of at range. Even if it impacts at optimum speeds, 70 percent of 5.56 mm bullets will not begin to yaw until of tissue penetration. 15 percent more begin to yaw after that distance, so up to 85 percent of rounds that hit do not start to fragment until nearly 5 in of penetration. Against small statured or thin combatants, the M855 has little chance of yawing before passing through cleanly and leaving a wound cavity no bigger than the bullet itself. The factors of impact angle and velocity, instability distance, and penetration before yaw reduce the round's predictable effectiveness considerably in combat situations. M855A1 The M855A1 Enhanced Performance Round (EPR) was introduced in June 2010. It features a lead-free 62 grain (4.0 g) projectile with a solid copper core, and is tailored for use in rifles with shorter barrels such as the M4 carbine. It provides more consistent performance compared to the M855. Deployment On 24 June 2010, the United States Army announced it began shipping its new 5.56 mm cartridge, the M855A1 Enhanced Performance Round (EPR), to active combat zones. During testing, the M855A1 performed better than M80 7.62×51mm NATO ball ammunition against certain types of targets (particularly hardened steel). However, this was due to the addition of the steel penetrator to the M855A1 projectile compared to the standard lead-alloy core