From M16 to M16A1
From M16 to M16A1 M16 M16A1 Caliber: 5.56×45mm M193 On February 8, 1964, the United States Air Force officially designated the XM16 as the "United States Rifle, Caliber 5.56mm, M16". Due to the AR-15 's charging handle only having the function of pulling the bolt carrier group back, without assisting in chambering a round, and the bolt carrier group being relatively lightweight, if for any reason the bolt carrier group fails to fully close, the bolt will not lock, leading to concerns about this issue. Therefore, the experimental version adopted by the Army added a bolt assist device (bolt assist handle, also known as the "forward assist") to the M16, and it was designated as the XM16E1. Thus, the main difference between the XM16E1 and the M16 is whether there is a piston-shaped bolt assist handle on the right side of the receiver. In addition, the surface of the M16 receiver is smooth, while the XM16E1 receiver has multiple serrations on the right side to acco...