M16A1 HBAR (Colt Model 621) - During the 1970s and 1980s, Colt wanted to sell not just standard M16 rifle and CAR-15 carbines to foreign military customers, but also wanted to supply support weapons. They put together the Model 621, aka M16A1 “HBAR” (Heavy Barreled Assault Rifle - not the same idea and the HBAR target rifles much more commonly seen) as a sort of LMG sister to the M16A1 rifle. It was essentially the exact same idea as the RPK - a support machine gun with parts interchangeability and identical handling to the standard infantry rifle. A small number were made in the 9 million serial number range, but no contracts were ever made to sell them in significant numbers. A few, like this one, eventually came out of Colt and into the civilian collectors’ market.

Colt Model 750/Model 950 (USA) & Colt Canada C7/C7A1 LSW - During the 1980s Colt decided to expand on the basic ideas that had been developed in the WAK and BRL guns. The weapon was essentially a modified M16A1 with a new square handguard to cover the enlarged straight gas tube and almost 1 inch thick heavy barrel to make the barrel less susceptible for overheating and hence increase the sustained or effective rate of fire capability, a carry handle on top of the handguard, with a hydraulic buffer assembly and the ability to fire from an open bolt. The chrome-lined barrel was permanently fixed to the receiver and could not be replaced in the field. An angled foregrip was added to the handguard to improve handling as an automatic rifle. Rear sights later featured on the M16A2 were also introduced, and the weapon could only fire in fully automatic firing mode. Unlike many M16 variants, it fired from an open bolt, necessitating the removal of the forward for operating safety. Colt initially packaged these weapons with the MWG 90-round "snail drum" (later replaced with the Beta System C-Mag). Colt had also originally used the M60 Machine Gun bipod, but switched this to a proprietary design that was lighter for the subsequent Model 750.

The Colt Model 750 was an improvement of the basic principle of the Colt LMG, developed jointly by Colt and Diemaco with an eye to Canadian Army sales. The improved version featured all A2 parts and is essentially the same as the preceding variant externally except for the redesigned vertical foregrip, now of a ribbed straight cylindrical style. This weapon was marketed by Diemaco as the C7 Light Support Weapon (LSW) or simply as the LSW. The Netherlands Marine Corps designate it as "LOAW" (licht ondersteunend automatisch wapen/light supporting automatic weapon) and the Danish military as "LSV M/04". The LSWs used by the Netherlands Marine Corps and the Danish military like many M16 variants fire from a closed bolt and feature semi-automatic and fully automatic firing modes and a forward assist. With its 5.42 kg (14.5 lbs) the C7 LSW is relatively light and as it uses 5.56×45mm NATO ammunition fed from STANAG magazines, like assault rifles and carbines that are fed in the same way, ammunition is easy to redistribute between riflemen if the operator runs out of ammunition. The lack of belt feed and quick barrel change options limits the C7 LSW and similar magazine fed light support weapon's rapid rate of fire.

Colt and Diemaco further improved on the design, adding a flat top carry handle and a further improved bipod to the weapon in the 1990s. Colt refers to it as the Model 950, but markets it as the Colt Automatic Rifle, and until their purchase by Colt, as the Diemaco LSW. Because of the Colt-Diemaco partnership on this system, it was the only weapon in the Diemaco product line to feature M16A2-type range and windage adjustable rear sights, and when modified a detachable carry handle with M16A2 fully adjustable rear sights (the majority of Diemaco's product line had modified M16A1-type rear sights, and they actually developed a detachable carry handle with modified A1 rear sights). A maple leaf is stamped on the lower receiver of current Colt Automatic Rifles.