M55K carbine

The M55K carbine is a compact version of the M55 SCAR used by the UNSC Marine Corps. It was designed by Misriah Armory and is manufactured by Heckler & Koch.
== Overview ==
The M55K is a selective fire, gas-operated, fully ambidextrous bullpup carbine derived from the M55 SCAR. The trigger and safety system were, as in the parent design, retained from the M37 rifle, consisting of a Spz-kr type progressive trigger (pulling the trigger halfway produces semi-automatic fire, pulling the trigger all the way to the rear produces fully automatic fire) and a safety mechanism (cross-bolt, button type), located immediately above the hand grip.
The M55K is fed from box magazines with a 40-round cartridge capacity using polymer-cased, high-pressure 6.8x43mm ammunition. The magazine catch/release button is installed symmetrically in the pistol grip, in front of the magazine well. The M55K retains the "flush-lock" magazine well of the SCAR, requiring the magazine to be pulled out manually once the catch has been pressed.
The M55K has a 407mm barrel, giving it an effective range of 300 meters, dependent on fire mode. It also features a built-in electronics suit that includes a standard smart-linked electronic targeting system, digital ammunition counter, and a magnetic compass for orientation. The rifle has a cyclic fire rate of 650 rounds per minute.
== History ==
The M55K was used by Special Forces units during the Insurrection and the Great War. SPARTAN-II Blue Team used M55Ks during Operation: TALON and the Battle of Chi Ceti. The M55K also became the main rifle used by the SPARTAN-III Program.