Colt basically made this Model 635 as a blowback action submachine gun based off of the AR-15 (which they bought the rights for from Armalite and Eugene Stoner, and manufactured for the military). The 635 has a cyclic firing rate of 900 rounds per minute, but only has a 32 round magazine capacity.
Leave it to Colt to just copy other designs, and not invent their own crap.