The BRN-601A(R) Complete Upper Receiver is back! Styled after the original Model 601, introduced in the late 1950s, the BRN-601A(R) has distinct features, only found on those early AR-15 rifles. Starting at the muzzle, the "duckbill" flash hider is retained by a proper split washer of the proper size. The flash hider is attached to a lightweight 20 inch barrel, found on AR-15 variants through the M16A1. The 1-12 twist stabilizes 55gr and lighter projectiles extremely well, while the 20 inch barrel provides plenty of velocity. The front sight base is not F-marked, meaning the round, tapered front sight post is properly in line with the carry handle rear sight. Solid green Mfg: Brownells