MA5C assault rifle

The MA5C Assault Rifle is a weapon to be introduced in Halo 3, essentially a redesigned and balanced version of the older MA5B Assault Rifle from Halo: Combat Evolved. Bungie has confirmed that it is more accurate than the MA5B, but this comes at the expense of ammunition, only carrying 32 rounds per magazine. however, they have also stated that it is more useful and versatile than ever, and that it is much more balanced. This new weapon can be seen in the Halo 3 trailer, and the recent ESPN Halo 3 advert.

Theories
It is thought the MA5C uses 7.62 Magnum rounds, instead of standard size. The reduced magazine may indicate more damage, and the MA series or any firearm series cannot convert into other ammo types, only to the extent of magnum sizes and shredder rounds. With the longer barrel, the rounds can be more utilized, seeing as how Magnum bullets have more gun powder equaling a higher voloctiy, adding the longer barrel will optimize range. The connection between the M6C Magnum and MA5C is the C, which may indicate it as magnum rounds for the Assault Rifle's side.

More likely, the C designation is merely to differentiate it from other weapons of the series such as the MA5B. rather than firing magnum rounds, it will likely make use of the 7.62x51mm Full Metal Jacket-Armor Piercing (FMJ-AP) ammunition used in Halo 1, or the 7.62x51mm Shredder rounds mentioned in the books, said to be interchangable with each other.