This 16" 5.56mm upper started life as a CA-legal Bushmaster patrol rifle back in the 1990's. It features a pinned and welded AK-style muzzle brake, on a 1/8 twist HBAR carbine-gassed barrel. Recently, the original upper was swapped out to a BCM Blem M4-style flattop upper. Original BCG and a GI-style charging handle also included.