M634 Experimental High-Powered Semi-Armor-Piercing (abbreviated M634 X-HP-SAP) ammunition is a type of United Nations Space Command rifle projectile that is made specifically for the UNSC BR55 Battle Rifle series. The round's metric dimensions are 9.5x40mm, compared to the 7.62x51mm NATO rounds used in the MA5 Series of UNSC Assault rifles, and was introduced into the UNSC Marine Corps along with the BR55 Service Rifle. However, while the M634 X-HP-SAP does do more damage than the 7.62x51mm NATO against vehicles, it is still not a very effective round at damaging or stopping vehicles.