ARC-920 railgun

The Asymmetric Recoilless Carbine-920 (abbreviated ARC-920 or known simply as the Railgun) is a compact-channel linear accelerator weapon used by the United Nations Space Command. It was designed and manufactured by Acheron Security.

It fires high-explosive projectiles accelerated to an incredible speed. The explosive yield contained in the round adds to the kinetic force of the impact, making the weapon effective against both infantry and armor.

List of appearances

 * Halo 4

Trivia
The name may be a 7 reference, since 9-2=7.