Not all ammunition is the same and different types and calibers come with important tradeoffs. Key Point: In the 1980s, both services shared the same ammunition. Those bullets were deemed insufficient, but the Marines and Army ended up choosing different ammo to replace the old kind. In Mark Bowden’s book, Black Hawk Down, he describes an incident where a soldier’s CAR-15 5.56mm carbine failed to put down an enemy combatant despite multiple hits to center mass. The ammunition used by the soldier was the M855 “green-tip” projectile, adopted by the U.S. Army and Marines in the 1980s.