| Production information
|| Ballistic (Direct Fire)
| Tech Base
|| Inner Sphere
| Year Availability
|| 2490 (LC)
| Technical specifications
| Minimum Range
| Short Range
| Medium Range
| Long Range
| Critical Slots
| Ammo Per Ton
| Cost (unloaded)
| Ammo Cost (per ton)
| BV (1.0)
| BV (2.0)
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.
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.
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.
The Deathgiver is known to fire 12cm (120mm) rounds.
||Typically used in
|| King Crab
Defiance 'Mech Hunter
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.
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.  
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.
The Tomodzuru-series has a massive 200mm barrel.
||Typically used in
Zeus-36, Mark III
||Typically used in
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. 
- Caseless Autocannon/20: A smaller and lighter version of the Autocannon/20 specifically designed to use caseless ammunition, giving it three times the ammunition capacity per given mass, along with a size and weight profile just slightly larger than the Autocannon/10. However, it has one critical design flaw that led to it being phased out in favor of a more modern variant of Caseless munitions; though these newer munitions are not as lightweight as their counterparts, they can be used with a simple modification to existing Autocannons and are far less prone to explosions in the event of a weapon jam.
- ↑ Interstellar Operations, p. 118, "Prototype Dates For Basic Weapons Table"
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 Tech Manual, p. 207
- ↑ 3.0 3.1 TechManual, p. 317, "Inner Sphere Weapons and Equipment BV Table"
- ↑ TechManual, p. 208, "Autocannon Munitions"
- ↑ Objective Raids, p. 155, "Ramora - United Outworlders Corporation"
- ↑ 6.0 6.1 6.2 6.3 Technical Readout: 3039, p. 86 "Combat Vehicles - Demolisher Heavy Tank
- ↑ Technical Readout: 3026 Revised, 46
- ↑ Technical Readout: 3039, 56
- ↑ Storms of Fate, Ch. 25
- ↑ Technical Readout: 2750, p. 54-55
- ↑ Objective Raids, p. 128, "Produced Kali Yama Weapons Components"
- ↑ Technical Readout: 3050 Upgrade, p. 58 "HBK-5M Hunchback"
- ↑ Technical Readout: 3055 Upgrade, p. 58 "THR-1L Thunder"
- ↑ Storms of Fate, Ch. 11
- ↑ 15.0 15.1 Technical Readout: 3050, p. 152 "Inner Sphere - Heavy 'Mechs - AXM-1N Axman"
- ↑ First Somerset Strikers, p. 73 "ComStar Technical Briefing - Inner Sphere BattleMechs - AXM-2N Axman"
- ↑ BattleTech Compendium: The Rules of Warfare, p. 127 "Technical Readout: AXM-2N Axman"
- ↑ Technical Readout: 3050 Upgrade, p. 70, "Axman"
- ↑ 19.0 19.1 Technical Readout: 3039, p. 159
- ↑ 20.0 20.1 Technical Readout: 3025, p. 110
- ↑ 21.0 21.1 Technical Readout: 3025 Revised, p. 104
- ↑ 22.0 22.1 Technical Readout: Succession Wars, p. 154
- ↑ Technical Readout: 3026, pp. 32-33, "Saladin Assault Hover Tank"
- ↑ Technical Readout: 3026 Revised, pp. 36-37, "Saladin Assault Hover Tank"
- ↑ Godfather
- ↑ Technical Readout: Succession Wars, p. 168
- ↑ 27.0 27.1 Technical Readout: 3026, p. 46 "'MechBuster Fighter"
- ↑ 28.0 28.1 Technical Readout: 3026 Revised, p. 50 "'MechBuster"
- ↑ Technical Readout: 3039, p. 184, "MechBuster"