From Halopedia, the Halo wiki
Developed as a response to the Insurrection and the Covenant, the weapon is issued to UNSC vehicle and aircraft crews, security personnel, and Spartans who expect close-quarters combat, and has been adopted by a number of UEG security forces.
The M20 is visually similar to its predecessor, though it differs in using a new high-velocity armor-piercing round that increases the amount of kinetic energy imparted to the target, specifically developed to counter the proliferation of military-grade armor among Insurrectionist cells and as a response to Covenant energy shield technology. The weapon uses top-mounted magazines of cased ammunition rather than the side-mounted magazines of caseless ammunition used by the M7. Otherwise, the weapon is very similar, featuring an adjustable grip under the weapon and a telescoping stock which can be retracted, allowing the weapon to be fired one-handed. Although the most commonly issued model features a CQB sight attachment, the weapon also accomodated an array of extended barrels, sound suppressors, laser targeters and recoil stabilizers. The weapon is also compatible with kinetic bolts that impart more kinetic energy to the target, and can be equipped with an energy bayonet.
Changes from M7 SMG in Halo 2: Anniversary
Halo 5: Guardians variants
List of appearances