MA2B assault rifle
From Halopedia, the Halo wiki
Template:Weapon Not to be confused with the MA5B, the Assault Rifle from Halo: CE or the MA5C from Halo 3
The MA2B Assault Rifle is a cut-down version of the standard MA5B Assault Rifle. The MA2B is tough and reliable. It has electric targeting, an ammo supply indicator, and a recoil-reduction system. The MA2B can deliver an impressive fifteen rounds per second and uses .390 caliber ammunition. The Spartans used these weapons periodically when they were required to carry very little ordnance for a mission. In fact, John used an MA2B Assault Rifle on his very first real mission. They used these rifles first when capturing Colonel Robert Watts of the Eridanus Rebels.
One of the possible main reasons that the Spartans chose the MA2B instead of the MA5B for the mission is because of the weapon's large magazine. Sam was seen loading a extended magazine into the receiver. This means that they could carry more ammo with less magazines. This was important, as too many magazines would clink together and would alert the security forces. Since it uses the smaller .39 Caliber round, it would have been incompatible with any ammo they would have picked up. The only reason they may have used it is because it would allow them to go for longer periods without reloading. Rather than just holding the trigger. You can use short controllered round bursts
