LAC - Light Autocannon.
The first Light Autocannon were prototypes created by the NAIS during the Clan Invasion. They didn't see widespread production until after the NAIS was destroyed by the Word of Blake's assault on New Avalon. Despite the advances of the NAIS, only the lightest two autocannon were effective weapons.
The LAC/2 and LAC/5 trade some range for a weight reduction of approximately 20%. This allows combat units to carry more weapons, ammunition, or armor, and still use the specialized autocannon rounds (Precision, Flechette, and Armor-Piercing) developed for the AFFS. The AFFS is the largest user of the Light Autocannon, but Imperator Automatic Weaponry has introduced the weapon to the Free Worlds League Military
Currently there are only two types of Light Autocannon:
HVAC - HyperVelocity Autocannon.The Hypervelocity Autocannon (HVAC) family of weapons is based on the Autocannon. While they have the same damage classes, they're capable of firing much further. However, in order to obtain the increased ballistic range, the hypervelocity ammo is larger and uses a unique type of propellant, reducing the number of shots per ton of ammo along with a couple other drawbacks, such as a chance of the weapon exploding, and a thick smoke trail every time the weapon is fired.
Like Ultra or Rotary autocannons, Hypervelocity autocannons are unable to make use of special munitions.
As of 3059 there are three Hypervelocity Autocannon types developed by the Capellan Confederation:
Source: Sarna.net