Ballistic Weapons - AC-20
The Autocannon is a direct-fire ballistic weapon, firing HEAP (High-Explosive Armor-Piercing) rounds at targets either singly or in bursts.
Different manufacturers and models of autocannons have different calibers (25mm-203mm) and rates of fire. Due to this, autocannons are grouped into generic "classes" of autocannons with common damage ratings, with Autocannon/20s doing massive damage while having very short range.
An example of the rating system: the Crusher Super Heavy Cannon is a 150mm weapon firing ten shells per "shot", while the Chemjet Gun is a 185mm weapon firing much slower, but causing higher damage. Despite their differences, both are classified as Autocannon/20s due to their damage output.
An Autocannon/5 can use special munitions to increase its effectiveness.
Description provided by Sarna.Net
In MW:PR 3051 the AC/20 deals 20 damage total, regardless of the amount of projectiles fired from the weapon. Depending on the mech, some AC/20s will shoot a single round, while others will shoot multiple per cassette.