M6B magnum
From Halopedia, the Halo wiki
The M6B Magnum Sidearm[1] is a United Nations Space Command ground firearm.
It is a variant of Misriah Armory's M6 Series of sidearms, and is noted for its comfortableness and its electronic KFA-2 x2 scope. However, it sees only widespread distribution in civilian security forces, not mainstream UNSC military units.
The M6B Handgun is believed to fire 12.7mm x 40 projectile ammunition, possibly semi-armor piercing (SAP).
