Magnetic Accelerator Cannon (MAC) 

A large railgun type weapon frequently used in the Halo universe. Sizes vary, from a handheld one shot anti-personnel weapon, to the main weapon of most of the frigates, destroyers, cruisers, etc (e.g UNSC Pillar of Autuum) to the largest, most powerful type, the "Super MAC", a massive railgun mounted on a space station capable of firing its projectiles at speeds close to 4% the speed of light. (e.g. Cairo Station, Halo 2). Said projectiles are made from extremely dense metals, such as depleted uranium, and despite the disadvantage of having to charge the weapon for every shot, the sheer kinetic impact velocity of these projects can do extreme damage to most targets.

“That Magnetic Accelerator Cannon (MAC) gun can put a round clean through a Covenant Capital Ship" - Sergeant Major Johnson describing the sheer firepower of Cairo Station to the Master Chief John-117.

Magnetic Accelerator Cannon (MAC) by Breaking_Bad_RV January 10, 2015