It's a cross between a "sniper rifle" and an main battle rifle. Often called a designated marksman rifle. If you will, a medium range precision weapon mostly for urban environments. Longer range work is done typically with a bolt action rifle or a M82A1.
It can be a pain getting match grade ammo through the military system. Typically we just get normal ball ammo. For the M82A1, I got boxes of linked .50 cal ammo intended for the M2.