From Halopedia, the Halo wiki
The MK50 Sidekick is a powerful and compact semi-automatic handgun which fires 10mm rounds from a 12-round detachable box magazine. It is significantly distinctive from the UNSC's typically-employed M6 series in both form and function, as it lacks the hand-guard and typical smart-linked optic of the latter series, as well as being chambered in a substantially smaller ammunition type than the M6's 12.7mm rounds. The design of the MK50 is relatively simplistic, with a segmented slide and basic, analogue ironsights. A safety switch is present on the left side of the weapon, above the trigger-guard. Emerson Tactical Systems' emblem is worked into the grip. The MK50 used in 2560 by John-117 featured a matte black and olive green finish.
The MK50 can hold 12 rounds with at least 72 rounds in reserve. It appears to be headshot-capable and features a very rapid reload animation.
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