Heavy Cannon vs Auto Cannon

• At medium to long range, the Heavy Cannon in general has 50% better firepower (effective damage per turn) than the AutoCannon against lightly armoured targets. This advantage increases further against more heavily armoured targets.
• The HC is significantly cheaper to own and operate than the AutoCannon - around half price.
• The HC is even more superior in reaction fire (snap fire only, no auto) firepower at medium to long range.
• Generally the HC has the best first-shot-kill probability (except at close range) - very important when aliens can reaction fire with plasma weapons on Auto against lightly armoured troops!
• Heavy Cannon is the most powerful "safe" sniper weapon vs well-armoured targets. (The Rocket Launcher is more lethal but in no way "safe" for friendly targets or loot). The Pistol is slightly more lethal, but only against very lightly armoured targets. The HC is superior to all others in this regard, even the Laser Pistol. It is only beaten when the Laser Rifle appears.
• HC generally is better for point destruction of hard terrain than AC (both AP and HE). HC will tend to destroy objects that the AC would not. However, the AC on Auto-Fire will cover a greater area destruction and is better for clearing large amounts of light or medium cover.
• The HC can step up to tackling Mutons, with some degree of success. At medium range and above the HC-AP has double the Autocannon's effective firepower against Mutons, and HE (the best round vs Mutons) is 20-40% more powerful (20% vs AC auto, 40% vs AC snap).
• Except at close range, AC-HE or AC-AP on auto is so inaccurate as to be barely more effective than snap shot. HC snap fire is much more effective than AC snap or auto.
• However in cases where AC-HE auto can be used without any regard to accuracy (point blank range in Power Armour, or short range with targets against a strong wall), total firepower is about 60% higher than HC-HE.
• Similiar to the walls, with a height advantage, the ground itself makes Autocannnons with HE much more powerful. Shooting from higher ground/ Flying Armor will turn an Autocannon with HE into an extremely deadly weapon.
• However, HE auto has the unwanted side-effect of destroying a lot of precious alien equipment, when an enemy dies from the first shot, drops his equipment and corpse, and the 2nd shot wipes out all the bounty.
  • Actually, since plasma weapons (amongst the more valuable alien items) are difficult to destroy, this isn't quite as bad an issue as it may seem. The Auto Cannon will do 44 damage vs objects at ground zero, so a dead on hit on the killed alien will still leave its primary weapon. (Damage vs. objects is not randomized.) At one space away from ground zero, a Blaster Launcher will also survive. However, the body, any grenades, and any spare clips will be destroyed unless your soldier botches the shot by 3 squares or more (2 squares for the body), Alien bodies are each worth half the cost of a replacement soldier. And the extremely valuable Mind Probes - worth 5 soldiers - are very easily destroyed. Using HE inside a UFO is a very bad idea, as there are lots of very valuable items - not just in financial terms - that are easily destroyed by HE.
• Similarly, the AC becomes more powerful when firing in a target rich environment. If there are multiple enemies inside the firing arc, firing at the center enemy will likely either hit the intended target or the other unintended targets.
• Another advantage the Auto Cannon has over the HC are its 2.33 times greater ammo capacity. (But surely it is better to run out of ammo than to run out soldiers. XCom fights firefights, not seiges. Lethality is more important than attrition or endurance. Also, since the AC is usually used in burst mode, and the firepower comparisons compare AC bursts to HC snap fire, the AC actually has less ammo capacity from that perspective.)
• Conversely the main downside of the HC is the 6-rd ammo limitation, and its implications for Encumbrance, total ammo capacity, reload frequency, diversity of ammo types per soldier, inventory slots used, and use of the 80-item limit. For small squads (eg 6 man) this will lead to Weight/Encumbrance problems carrying enough ammo to finish the mission. For large squads (14 man) this is less of a problem but still puts quite a strain on the 80-item limit. The AC does suffer from the same problem, though to a slightly lesser extent.
• The AutoCannon has definite specialist roles where it is superior to the HC, such as illuminating with IC, or fighting Reapers with HE. AC-HE on auto can also be more effective for mass clearance of deep (but light) cover.
• Sometimes clearing said cover will result in alien deaths. The AC is the best human weapon for "suppresive fire" or "blind fire" or tactical area bombardment. If you suspect there is an alien in the general area but can't see him, the AC-HE is your best friend.
• The AC-HE is possibly the best weapon for training up Firing Accuracy, since it has the largest (theoretical) amount of hits in 1 turn of fire. 1 burst of auto-fire on a Reaper will be enough to max out a soldier's accuracy experience gain potential for that mission, if all 3 shots hit all 4 squares.
• If exploiting the Incendiary Exploit, the Autocannon gains relative to the HC, as it can fire more rounds (doing fire damage to multiple units each time), and arguably it can make more effective use of the limited number of map squares that can be on fire, due to its smaller burst radius.

• The biggest drawback to all heavy weapons is weight restrictions or the resulting TU penalty from encumbrance. For the HC 81% of starting rookies can carry it (unencumbered) with 1 extra clip, 52% with 2 extra clips and 24% with 3 extra clips. As for the Auto-Cannon, 81% can carry it with 1 more clip, 57% with 2 more clips and 33% with 3 more clips. (Due to a bug, the first clip of any weapon, usually AP, is loaded automatically and "weight free" during the Equip Troops phase, unless you change or unload it, so this adds +1 clip to the preceding figures.)

Note: "Firepower" as used here is defined as "average armour-adjusted damage delivered on target per unit of time".

See Also

Weapon Analysis