XM-177

Colt marketed the Model 609 submachine gun, otherwise known as XM-177 Commando (although it is not a true sub-machine gun, since the latter fires pistol ammunition). It has a sliding, retractable buttstock, foward assist (for seating the bolt into chamber), a 10 inch barrel, which has smaller round handguards and a unique "sound and flash" suppressor. This gun was given the US Army designation of XM-177E1. The US Air Force purchased the Colt Model 610, and designated it GAU-5/A. This differed only in not having the forward assist.

After fielding it, improvements were suggested. Colt then produced and sold the Model 629, in which the barrel was lengthen to 11.5 inches and got a redesigned "flash and sound" suppressor (behind the new suppressor a washer was added to enable the user to fire rifle grenades). The US Army designated this weapon the XM-177E2. The US Air Force purchased the Colt model 630 (no forward assist) and it was classified GAU-5A/A. Soldiers and sailors called this the CAR-15 (which is actually a different Colt firearm). However, the designation of CAR-15 stuck and these early models are still referred to today as the CAR15.

Colt improved the basic design in the early 1970s. The barrel was lengthened to 14.5 inches. Now using a standard rifle suppressor and having a bayonet stud (for the attaching of the M-7 Bayonet), Colt numbered this 653. The US Army and US Navy procured some in small numbers for SOF units, but did not offically adopt it. It was also referred to as the CAR-15. These various models were used until the mid-1980s when the M-16A2 was adopted. Along with the new rifle came the new M-855 ball round.