One of the most popular rifle configurations on the market is the M4A1-style AR-15, and these guns are based on the military-contract carbines produced by Colt in the first place. Now, you can get a genuine Colt-produced barrel for your M4A1 carbine clone. Each Colt M4A1 AR-15 Barrel, chambered in 5.56 NATO, features six-groove rifling with a 1:7-inch rate of twist. The barrels include M4-style feed ramps and have a chrome lining that prevents corrosion. Each barrel is set up for a carbine-length gas system and features 1/2""-28 TPI threading at the muzzle. Colt's M4A1 AR-15 Barrels are available in 14.5-inch lengths and can be had as a stripped barrel, complete with barrel extension, or as an assembly that includes a barrel nut, front-sight tower, post and sling swivel.