AutoCannon/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.

This autocannon class can decapitate any 'Mech with one good hit to the head, regardless of the weight class. The head of any 'Mech cannot mount little more than a ton's worth of standard armor. The AC/20 is capable of ripping nearly a ton and a quarter of armor off a 'Mech in any given volley (or shot, based on the model). This is enough damage to take down even the heaviest of 'Mechs if aimed well. Only Hardened Armor or Ballistic-Reinforced Armor can save a MechWarrior from a hit from this class of cannon to the head, if the full value of armor is mounted on the head of the 'Mech.

An example of the rating system: the Crusher Super Heavy Cannon is a 150mm weapon firing ten shells per "round" while the Chemjet Gun is a 185mm weapon firing much slower, and causing higher damage per shell. Despite their differences, both are classified as Autocannon/20s due to their damage output.

Ammunition
A standard AC/20 can fire multiple types of ammunition, most of which were developed by the Federated Commonwealth in order to make their large supply of standard autocannon more useful in the age of Ultra and LB-X autocannon.

Models
The Autocannon/20 is manufactured on the following planets:

ChemJet Gun 185mm
The titanic ChemJet Gun uses a popular propellant system that mixes two chemicals in suspension to propel its huge shells out of the barrel. This produces an enormous amount of heat, to the point that on the Mk I model of the Demolisher tank that the crews had to wear special coolant suits, though the later Mk II version solved this problem by channeling most of the ejection gases through the barrels.

Crusher SH Cannon
Mounted on the Quickscell Hetzer Combat Vehicle, this weapon fires shells in the 150mm range in ten shot bursts.

Deathgiver
The Deathgiver is known to fire 12cm (120mm) rounds.

Kali Yama Big Bore
The Kali Yama Big Bore is an Autocannon/20 model manufactured in the Free Worlds League and exported to the Capellan Confederation.

Luxor Devastator-20
Examples of the 120mm Luxor Devastator-20 gained a reputation that they were so prone to jamming on the early test models of the AXM-1N Axman that the designers ultimately came up with an alternate LRM-15 armed AXM-2N variant.

Pontiac 100
The Pontiac 100 is famously known for massive firepower, but some models occasionally display ammunition feed problems when mounted to the Victor BattleMech.

Scarborough Original 20
Originally developed by Scarborough Limited, though the Scarborough Original 20 Autocannon did experience some initial developmental problems, the resulting weapon is equivalent to 200mm autocannons produced by other companies in the massive amount of damage it can inflict.

Tomodzuru
The Tomodzuru-series has a massive 200mm barrel.

Zeus-75 Mark IX
The mammoth Zeus-75 fires a four-round burst of hypervelocity depleted uranium armor penetrators (HDUAP) capable of destroying most 'Mechs up to 70 tons in a single salvo.