The M90 has a capacity of 900 rounds, all loaded in a single, continuous belt, and fires in minimum bursts of 3 rounds. The entire 900-round belt can be emptied in significantly less than one minute. The weapon has three barrels, and is exceedingly heavy, slowing the user down while the weapon is readied. It fires armor-piercing rounds at an extremely high rate of fire, making it effective against small, fast-moving, hard-to-hit targets as well as durable, armored targets that smaller weapons may be ineffective against.
The M90 Minigun has two modes of fire. The standard mode of requires the operator to hold the trigger down until the barrels spool up to speed. This increases the time required to engage a target, and may have lethal consequences in high-threat, close quarters environments. The second fire mode keeps the barrels spooled. This means the weapon is ready to fire instantaneously, but the effect is quite noisy, and can alert nearby enemies to the presence of a minigunner.