My head is spinning.
The revised bullet construction was difficult to manufacture. When U.S. troops were heavily involved in ground combat in Iraq, Lake City Army Ammunition Depot could not supply enough “green” 5.56 NATO ammunition. The only manufacturer that could was Israeli Military Industries, Ltd. Due to PC concerns by the Bush State Department, IMI-produced ammo was shipped to the U.S. and only issued to U.S. troops. Lake City produced ammo went to Iraq for combat use. The reason: use of IMI ammo might “offend” Muslim allies!
Meanwhile, there were concerns that the “green” bullets posed heavy metal pollution problems for ground water. Red flags started to go up as early as 2003. By 2006, The Army at Camp Edwards, MA discovered the tungsten powder from the bullets was leaching into the sandy soil of the military reservation. A groundwater sample taken that year beneath one of the small arms ranges showed concentrations as high as 560 parts per billion.
Such was the Army's concern that it went back to using the earlier production M855 ammunition with lead and mild steel core. Production of the tungsten-nylon projectiles was suspended and Lake City went back to the older mild steel-lead core version.
Starting in 2009, the Army began issue of its new, second generation “green” 5.56 NATO cartridge, the M855 LFS (lead free slug). The new Lake City projectile uses a bismuth-tin core and uses an improved propellant, has reduced flash, increased velocity, and better aerodynamics. The new M855 LFS projectile does not use conventional FMJ construction. Unlike current M855, the dark gray steel penetrator of the new M855 LFS extends through the jacket nose. The M855 LFS was redesignated the M855A1 in 2010.