M6A magnum
From Halopedia, the Halo wiki
The M6A 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. However, it sees only widespread distribution in civilian security forces, not mainstream UNSC military units.
The M6A Handgun is believed to fire 12.7mm x 40 projectile ammunition, possibly semi-armor piercing (SAP).
