original military issue AR-15 / M16 rifle (circa 1965), with no forward assist and with the original three-prong flash hider
M16A1 rifle, with the forward assist, "bird cage" flash hider and the 20 rounds magazine (1967)
M16A1 rifle with 30 rounds magazine and a 40mm M203 grenade launcher attached (circa mid-1970s)
M16A2 rifle, with the heavy barrel, modified rear sights, spent case deflector, round handguards and modified pistol handle (circa mid-1980s