MercTech: Autocannons

General overview
Rather than the size of Autocannon it is the caliber that determines how much damage is dealt per round, which can range from 30mm - 210mm. The difference between autocannon classes is now the overall DPS, so an AC-10 will have roughly twice the DPS as an AC-5, even if both are firing the same caliber.

When any of the Autocannon variants receive a critical hit there is a chance that the barrel component of the weapon will be damaged. Should the barrel be damaged, it is highly recommended to stop using the weapon, as there is a chance of an ammo detonation during firing, which can cascade into an ammo bin explosion.

Standard Autocannon:
Standard Autocannons can now be toggled to fire at double the rate of fire. This will double your effective DPS, but should the weapon experience a jam, it can cause barrel damage, which can lead into the dangers mentioned above. Switching rate of fire should only be done in emergencies.

With smaller models originally entering production during humanity's expansion into the Inner Sphere, and larger models following the introduction of the battlemech, the high rate-of-fire Autocannons have completely replaced the old tank cannons that have existed since the 20th century. With each class of autocannon suited to specific roles, they have become a common sight throughout the Inner Sphere, surviving the fall of the Star League and the subsequent Succession Wars. While newer, more potent variants have begun to slowly replace these older ACs, the creation of specialty ammunition has extended their life somewhat, allowing a standard autocannon to more effectively pierce armor or engage aircraft. There is word of other ammunition types in testing, including some with limited guidance, and others effective against infantry through either clustered flechettes or incendiary warheads.

LB-X Autocannon:
While there was only the LB 10-X in the base game, Merctech adds the remaining autocannon classes, with calibers ranging from 50mm up to 190mm. Unlike the LBX ACs in the base game, which are available in slug and cluster versions, Merctech LBXs can switch freely between these two ammo types, provided both are present in the mech's loadout.

An advanced variant of the autocannon created during the Star League-era, the LBX autocannon is capable of firing a special cluster ammunition, which releases scattered submunitions useful for exploiting openings in an enemy's armor and damaging internal components. The ability to fire standard slug munitions to open holes in armor and then follow with cluster ammo to exploit them makes the LBX AC a potent weapon. While the Star League had only developed this technology for the class 10 AC, the Clans had managed to adapt it to the remaining classes, in which captured examples would be reverse-engineered to allow the nations of the Inner Sphere to produce them themselves.

During the savagery of the Succession Wars, the LB 10-X would become LosTech until after the discovery of the Helm Memory Core, when it would re-enter production just before the Clan Invasion.

Ultra Autocannon (UAC):
Much like the LB 10-X was for that type of AC, only the Ultra AC-5 was present in the base game, with Merctech adding the remaining classes. Unlike in the base game, where UACs can fire again during cooldown, Merctech UACs have a fire-rate toggle that allows them to fire two rounds per cycle, doubling effective DPS. The weapon has a chance to jam when firing in this mode, although unlike standard ACs, there is no danger to the weapon's components no matter how many times it jams.

Another advanced variant of the autocannon developed by the Star League, the Ultra Autocannon uses a magnetic feed and a multi-barrel assembly in order to effectively and reliably fire at an increased rate of fire for prolonged periods of time. While only the class 5 Ultra Autocannon was in production by the fall of the Star League, the Clans had adapted the technology to the other classes, including the devastating class 20 Ultra Autocannon. During the technological renaissance after the invasion, the Inner Sphere would reverse-engineer the other classes for their own use.

Like the LB 10-X, the Ultra AC-5 would become LosTech for a time, re-entering production before the invasion of the Clans.

Caseless Autocannon (CAC):
An experimental variant of the standard Autocannon, Caseless Autocannons load and fire caseless ammunition. Since caseless ammo is composed of a projectile surrounded by hardened propellant, rather than a much heavier metal casing, the ammo weighs considerably less than its standard counterpart. In addition, since there's no need to extract and eject casings, the related mechanisms are removed, reducing the weapon's weight by roughly 20%. The issues related to caseless ammo is its vulnerability to heat, as there is a small chance the ammo could detonate while being fed into the weapon, which can cause a feed jam and even damage the weapon itself.

Rotary Autocannon (RAC):
Developed by the Federated Suns after the Clan Invasion, Rotary Autocannons take the magnetic ammo feed and multi-barrel assembly of the Ultra Autocannons to their extreme, allowing Rotary ACs to fire up to an astounding six times the rate of fire of a comparable standard AC. One must make intelligent use of this feature, as the risk of a temporary weapon shutdown increases the faster the weapon fires. To date, only the class 2 and 5 Rotary Autocannons exist, the likely reason being that adapting this technology to the larger classes would produce a weapon too bulky to use on a battlemech.

There is word that the Clans are testing prototypes of their own Rotary Autocannons, likely based on Inner Sphere models taken as isorla.

Light Autocannon (LAC):
Introduced by the Federated Suns after the Word of Blake's attack on New Avalon during their Jihad, the Light Autocannon makes use of every piece of weight-reducing technology available to the Inner Sphere in order to significantly decrease the weight of the standard autocannon. While the Light Autocannons have less range than standard ACs of the same class, the extra tonnage saved is well worth this drawback, while still being able to use the various new munition types available to the standard ACs. Only the class 2 and 5 Light Autocannons have been developed, one possible reason being that the loss of effective range would prevent larger classed LACs from being viable weapons.

Protomech Autocannon (PAC):
Developed by Clan Blood Spirit during the Word of Blake Jihad, the Protomech Autocannon, inspired partly by the Inner Sphere Light Autocannon, is designed to be light and compact enough for use on Protomechs. While these autocannons, available in class 2, 4 and 8, would fulfill their role well, the Clans would also adapt them for use on battlemechs, where their light weight and compact size would make them perfect for use on light and tonnage-starved units.

Additional notes:
Spies in the Capellan Confederation report testing of autocannons using gelled propellants that are capable of firing projectiles at extreme velocities.