The MAC-10 (Military Armament Corporation Model 10, officially the M-10) is a compact, blowback operated machine pistol developed byGordon B. Ingram in 1964. It is chambered in either .45 ACP or 9mm. A two-stage suppressor by Sionics, was designed for the MAC-10, which not only abated the noise created, but made it easier to control on full automatic. The M-10 was built predominantly from steel stampings. A notched cocking handle protrudes from the top of the receiver, and by turning the handle 90° would lock the bolt, and act as an indicator that the weapon is unable to fire. The M-10 has a telescoping bolt, which wraps around the barrel. This allows a more compact weapon, and balances the weight of the weapon over the pistol grip where the magazine is located. The M-10 fires from an open bolt, and the light weight of the bolt results in a rapid rate of fire. In addition, this design incorporates a built in feed ramp as part of the trigger guard (a new concept at the time) and to save on cost the magazine was recycled from the M3 Grease Gun. The barrel is threaded to accept a suppressor, which worked by reducing the discharge's sound, without attempting to reduce the velocity of the bullet. At the suggestion of the United States Army, it also acted as a foregrip to inhibit muzzle rise when fired. Ingram added a small bracket with a small strap beneath the muzzle to aid in controlling recoil during fully automatic fire. The original rate of fire for the M-10 in .45 is approximately 1090 rounds per minute. That of the M11/nine 9mm is approximately 1250 rounds per minute, and that of the M11 .380 is 1380 rounds per minute.