What Type of Feed Ramps Are for the AR15?

Eugene Stoner designed the Armalite AR15 rifle during the 1950s as a select-fire (semi- and full-automatic) service rifle for use by military forces. In 1959, Armalite sold the design to Colt, who produced it as the U.S. military-issue rifle. Colt also developed a semi-automatic-only version for sale to civilians. The AR15 has been modified further into two pistol-cartridge (9mm) designs. The AR15 uses four different feed-ramp patterns to provide a smooth transition of cartridges from the magazine to the chamber. These variations reflect the needs of different ammunition types.

  1. Standard AR15

    • The original AR15 design did not include feed ramps. The M193 (55-grain bullet) and M855 (62-grain bullet) of the time typically functioned reliably without ramps.

    M4 Carbine

    • Colt designed the M4 Carbine in 1994 for military use. Its short, 14.5-inch barrel, coupled with a greater variety of available bullet weights, caused a tendency to jam (fail to feed) in early testing, so Colt added feed ramps to the design. The ramps consist of a cut-out area in the bottom of the barrel extension, and a corresponding relief in the floor of the upper receiver. Together, these cut-out areas form a ramp just ahead of the magazine to ease passage of the cartridge into the chamber of the rifle.

    Colt 9mm Carbine

    • The Colt 9mm carbine uses a different bolt design than the original 5.56mm rifle. Unlike the locked-breech design of the original 5.56mm AR15 and M4, the 9mm is a blowback design in which inertia is the only thing holding the bolt closed. An adapter block fits in the standard magazine well and positions a modified Uzi 9mm magazine in the rear portion of the well. Because of the shape of the 9mm cartridge and the distance it must travel to reach the chamber, the adapter block features a feed ramp on its upper surface. The ramp guides the cartridge to the chamber and prevents it from turning and causing a jam.

    Olympic Arms 9mm carbine

    • The Olympic Arms 9mm carbine, like the 9mm Colt, utilizes a blowback action. However, the bolt nose is tapered and fits into a cone-shaped barrel extension just behind the chamber. The cone acts as a feed ramp. In addition, the modified Sten magazine is positioned in the forward portion of the standard magazine well, so the cartridge does not have to travel as far as it does in the Colt design.