An accelerator is part of an action that speeds up its function by transferring kinetic energy from one part of the mechanism to another. ¹

For example, during the unlocking phase of the cycle of operation, the barrel extension in an M1917A1 Browning Machine Gun strikes the accelerator causing it to rotate to the rear. As the accelerator rotates it strikes the bolt. This speeds up the movement of the bolt to the rear. ²

A more detailed description of this cycle of operation can be found in FM 23-55 Browning Machine Guns, Caliber .30, M1917A1, M1919A4, and M1919A6 (pp. 36-45). It is available as a free download in a variety of formats from the Internet Archive ⇒.

guns that have an accelerator: ³

• • • • M1917A1 Browning Machine Gun
      • M1919A4, M1919A6 Browning Machine Gun

1. “Glossary ⇒.” Sporting Arms and Ammunition Manufacturers’ Institute. Ed. SAAMI’s Technical Committee. Web. 15-18 Jan. 2011.
2. “Chapter I. Mechanical Training, Section IV. Mechanical Functioning.” FM 23-55 Browning Machine Guns, Caliber .30, M1917A1, M1919A4, and M1919A6. Washington: United States of America War Office, 1945. 36-44. Print.
3. This is not a complete list.