Unidentified UNSC weapon
From Halopedia, the Halo wiki
Template:New Content Template:Weapon Infobox This unidentified UNSC weapon appears in the Halo 4 announcement trailer. In the trailer, John-117 grabs one such weapon floating in zero gravity and uses it to blow a piece of debris out of his way whilst escaping the exploding wreckage of the UNSC Forward Unto Dawn.[1]
Sized like an ordinary sidearm, the weapon appears to fire explosive munitions attached to the muzzle, reminiscent of rifle grenades. There is a pair of rails below the barrel, possibly for securing the grenade in place. The weapon's reloading mechanism resembles a breech-loading system; the weapon's upper half flips open and a new cartridge is inserted before closing the covering. Whether the weapon has other firing modes is unknown.[1]