The M6A Handgun[1] is a standard issue United Nations Space Command firearm.
Background
The M6A is a variant of Misriah Armory's M6 Series of sidearms pistols, and is noted for its comfort. However, it sees only widespread distribution in civilian security forces such as Law enforcement and Governmental security; not mainstream UNSC military units. This model began production around 140 years before 2552.
The M6A Handgun fires 12.7mm x 40 projectiles, and has a black polymer finish. Unlike other models such as the M6D or the M6G, it is not upsized to fit MJOLNIR armor.[2]