The selector itself had 360 degrees of motion, and could be moved either clockwise or counterclockwise, unlike with standard groups. Unlike the standard three-position group, the four-position group went from (going clockwise from the 9 o'clock position) safe, fully automatic, semi-automatic and finally burst. The Model 605B had no forward assist, but had a four-position selector switch (developed by Foster Sturtevant in December 1966) so that a user could select safe, semi-automatic, three-round burst, or full automatic modes of fire.

One prototype used a shorter handguard and a 16-inch (410 mm) long barrel. Because of the shorter barrel, no bayonet mounting lugs were provided. The only significant change from the M16 rifle was that the barrel was shortened to 15 inches (381 mm) in length, so that it ended just forward of the front sight base. It was an improved version of the AR-15 SBR, which was a shorter barrel version of the Colt Armalite AR-15. The Model 605A CAR-15 Carbine was a shortened version for situations where longer weapons could be unwieldy, such as aboard vehicles or helicopters. It was made in prototype form only and saw no sales.Ī semi-auto Bushmaster Dissipator barrel which uses a similar short-barrel, standard length hand-guard concept to the CAR-15 Carbine The CAR-15 Heavy Assault Rifle M2 was a belt-fed conversion of the standard CAR-15, with a heavy barrel and bipod attachment. It was designed to feed from 30-round box magazines. The CAR-15 Heavy Assault Rifle M1 was a heavy-barreled version of the standard AR-15 with a bipod attachment, intended for use as a Squad Automatic Weapon (SAW).

The principal difference between the Model 603 and Model 604 is that the former has a forward assist, allowing a user to manually close a stuck bolt. However, the United States military had already committed to purchases before Colt created the concept of the CAR-15 weapons system. The Model 603 CAR-15 Rifle, adopted initially by the United States Army as the XM16E1 and then later as the M16A1, and the Model 604 CAR-15 Rifle, adopted by the United States Air Force as the M16, formed the core of the CAR-15 family.

Ar15 carbine with 10 inch quad rail