Autocannon

An Autocannon (short for Automatic Cannon) is a fully-automatic weapon that fires projectiles of 20mm diameter or larger. Autocannons are essentially massive Machine Guns, feeding from a very large ammo supply and firing at a very high rate. They are devastating weapons on the battlefield, particularly against Infantry and Light Vehicles.

Autocannon Shells are not only large, but typically carry a small High Explosive warhead that detonates on impact, making each shell significantly more likely to damage the target even when missing it during flight. The fast velocity and explosive impact make them useful against light- and medium-armored vehicles, but they are typically incapable of penetrating Tank armor (with some exceptions).

The weight of the autocannon and its ammunition make it impossible to be carried by hand. Autocannons are typically found fitted on IFVs, a few APCs, Attack Helicopters, and even Jets.

In ShackTac, the term Autocannon is used for virtually all such weapons, no matter what caliber they have or what vehicle they are installed on. Exceptions include the terms "Vulcan", "Chain Gun", "Gatling Gun" or "Rotary Cannon", which are all sometimes used for rotary multi-barreled autocannons, but may also refer to multi-barreled Machine Guns like the Minigun.

Specifications
The Autocannon is the heaviest and largest sub-class of fully-automatic weapons, alongside the smaller Machine Guns, Assault Rifles, and others. It refers to any such weapon that has a caliber larger than 20mm, and some models reach 40mm or even higher in diameter.

Some Autocannons use a firing mechanism that is similar to smaller automatic weapons, utilizing the gasses expelled behind a fired projectile (in this case a Shell) to load the next projectile into the firing chamber. More modern Autocannons use a complex electrically-powered mechanism to perform the same task. The result, as with any fully-automatic weapon, is that pressing the trigger will continuously fire more and more projectiles until it is released (or until the ammunition runs out). Autocannons typically load their ammunition through a continuous belt of shells from some large internal storage chamber.

The firing rate of an autocannon varies greatly from model to model, and is primarily based on the number of barrels on the weapon:
 * Single-barreled ("true") Autocannons, such as those found on most IFVs, typically fire powerful shells at a relatively slow rate (~200/minute). Gunners may occasionally fire one shell at a time to achieve greater accuracy and ammo conservation.
 * Multiple-barreled Autocannons, such as those mounted on Jets, fire generally lighter shells at a significantly higher rate. For example, the powerful GAU-8 Avenger found on the A-10 aircraft fires at a rate of almost 4,000 rounds per minute. It is virtually impossible to fire single shells with such a weapon. To prevent over-heating, these autocannons have multiple barrels that cycle around rapidly, so that each fired shell travels through a "fresh" barrel.

Shells
Autocannons fire small bullet-like projectiles known as Shells. The shells fired by an autocannon are quite heavy compared to Small Arms bullets, and cause significant damage on impact by their sheer kinetic energy. Nevertheless, Autocannons are typically loaded with High Explosive shells, which cause a small detonation on impact that's typically comparable to a small Hand Grenade. This increases the area damage of each shell, so that it does not necessarily have to impact with the target in order to hurt it. Furthermore, with large numbers of shells impacting in close proximity during a single burst, the Autocannon can destroy several targets rapidly, or ensure the destruction of a single target.

Many autocannons are also (or sometimes exclusively) supplied with Armor Piercing (AP) shells, which rely entirely on kinetic energy to penetrate the target's armor. While they lack the power required to penetrate heavy armor (such as the front armor of a Tank), they are highly likely to disable external systems and/or destroy tracks; slip through a weak spot or vision portal; or weaken the armor slightly to perhaps allow subsequent shells through. In any case, anything lighter than a tank is at risk of armor penetration from these shells.

Vehicles Fitted with Autocannons
Autocannons are rather large and heavy weapons. Other than the barrel and firing mechanism, the 20+ millimeter rounds fired by Autocannons are also very heavy, and the high firing rate requires a large supply of them to sustain fire over time. As such, they are simply too large to be carried by Infantry or even Light Vehicles.

On the ground, Autocannons are most commonly carried by IFVs, including some heavy APC variants. They typically have a single barrel and a slow firing rate, although there are some notable exceptions to that rule.

In the air, Autocannons are an extremely common weapon on Attack Helicopters and Jets, and are mostly multi-barreled (though not necessarily fast-firing).

Single-Barreled
Single-barreled Autocannons are commonly found mounted on IFVs. The most common weapons of these type are installed on the M2 Bradley and the BMP-2. Both weapons have a relatively low firing rate (~200rpm for the Bradley, ~500rpm for the BMP), and fire a shell of similar weight (25mm for the Bradley, 30mm for the BMP). These weapons pose a very seriously threat to infantry and vehicles, all the way up to enemy IFVs. However they lack the penetrating power to reliably damage tanks, which is why both vehicle models are fitted with ATGMs to tackle such heavy threats.

The BTR-80A is a Russian APC carrying an autocannon similar to the model used in the BMP-2. It is therefore a very dangerous adversary, although easier to defeat due to its weaker armor. BTR-80As have begun appearing in ShackTac videos around 2018.

Single-barreled autocannons are relatively rare on Aircraft, which typically need a multi-barreled high RPM. Nevertheless, a single-barreled autocannon can be found on the Mi-28 and Ka-52, both using the same autocannon as the BMP-2.

Multi-Barreled
Multi-barreled Autocannons come in a very wide variety of models, differing not only in caliber but also in the number of barrels and (correspondingly) the rate of fire. They are also found on both ground vehicles and air vehicles, although far more common in the air for several different reasons.

The more uncommon ground-based model is the Vulcan, a 6-barreled 20mm weapon with an extremely high rate of fire (6,000 RPM, or 10 rounds per second). These are most commonly carried by the M163 Vulcan, a specialized IFV based on the M113 Armored Personnel Carrier. The high rate of fire more than compensates for the relatively light rounds. Vulcans in ShackTac typically use High Explosive rounds to increase their effect.

Some OPFOR ground vehicles use an interesting variant of the multi-barrel concept, called a Zeus. This is actually a ShackTac nickname for the ZSU family of Russian weapons, where several single-barrel autocannons are linked together to fire in unison. This gives the weapon a higher firing-rate than a single barrel, but without requiring a rotary mechanism. Zeus Autocannons can be stationary emplacements (usu. with 2 barrels) or mounted on various vehicles (usu. with 4 barrels) - most notably the Zeus Truck and the Shilka.

The vast majority of BLUFOR and OPFOR Attack Helicopters used in ShackTac are armed with a Multi-Barreled Autocannon as their "default" weapon. The autocannon is typically mounted on a turret under the nose of the aircraft, and may even be slaved to the gunner's helmet, firing at whatever target the gunner looks at when pulling the trigger. BLUFOR Helicopter autocannons have only a few barrels, and fire at a relatively slow rate comparable to the Single-Barrel models described above. OPFOR tends to use single-barreled autocannons on their helicopters. Helicopters may be able to switch between High Explosive and Armor Piercing ammunition, depending on the target.

Practically every combat Jet appearing in ShackTac missions is armed with an autocannon. Jets can use autocannons to combat each other as well as attack ground targets. To facilitate air combat against fast-moving targets, these autocannons have an exceptionally high rate of fire often coupled with a large number of barrels (3 to 7). These autocannons are somewhat less effective against ground targets, as they are difficult to aim precisely enough to repeatedly strike the target. Jet Autocannon ammunition is almost always High Explosive, as the jet must increase its probability to hit the target at all, at the expense of causing damage. Jets are also typically fitted with other weapons to tackle armored threats. A Jet with nothing but Autocannon ammo remaining will usually call Winchester and return to base to rearm, rather than staying in the area to expend this ammo.

Finally, special mention must go to the GAU-8 Avenger Autocannon, which is installed on the A-10 CAS aircraft. The Avenger is by far the most powerful autocannon ever installed on an aircraft. It has 7 barrels, and fires at a rate of 3,900 rounds per minute. The rounds themselves are tipped with depleted uranium, which gives them superior kinetic penetration ability. Such rounds, at such a high rate, can rip into medium armor with ease, and may even overcome Tank armor when striking the rear or top armor. The armor-piercing rounds are also mixed in with a smaller number of High Explosive rounds, and at that high firing rate the number of explosions in the target area is nothing to laugh at.