what is a M4 bolt carrier
The M4 carbine is a shorter and lighter variant of the M16A2 assault rifle. The M4 is a 5.56Ã45mm NATO, air-cooled, direct impingement gas-operated, magazine-fed carbine. It has a 14.5 in (370 mm) barrel and a telescoping stock.he M4 is a 5.56Ã45mm NATO, air-cooled, direct impingement gas-operated, magazine-fed carbine. It has a 14.5 in (370 mm) barrel and a telescoping stock.