The first M16 LMG was essentially a modified M16A1 with a new square hand guard to cover the enlarged gas tube, a carry handle on top of this hand guard, with a hydraulic buffer and a the ability to fire from an open bolt. An angled fore grip was added to the hand guard to improve handling as an automatic rifle. The first LMG layout can be seen in the patent awarded to Colt engineer Henry Tatro. Rear sights later featured on the M16A2 were also introduced, and the weapon could only fire on the fully automatic setting. Colt initially packaged these weapons with the MWG 90-round "snail drum" (This was before the introduction of the Beta Systems C-Mag). Colt had also originally used the M60 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 toward the Canadian Army (though they would eventually select the FN Minimi). The improved version featured all A2 parts and is essentially the same as original variant externally except for the redesigned vertical fore grip, now of a straight cylindrical style that is ribbed. This weapon was marketed by Diemaco as the Diemaco C7 Light Support Weapon (LSW) or simply as the LSW.

Colt and Diemaco further improved on the design, adding a flat top carry handle and a further improved bipod to the weapon sometime during the '90s. The new model number is 950 but is currently marketed as the Colt Automatic Rifle, and until their purchase by Colt, as the Diemaco LSW.