The Main Service Rifle of New Mother Base. a semi-automatic rifle carbine manufactured by U.S. firearms company Sturm, Ruger & Company, Inc. The rifle was introduced in 2009, marking Ruger's entry into the popular AR-15 market, and it would continue with a .308 AR-10 variant, the Ruger SR-762.It is one of several new AR-15 platform rifles to use gas piston operation. In January 2016 Ruger discontinued all SR-556 rifles. Motherbase picked up the pieces and modified it to be an All Purpose Rifle capable of Cartridge swapping between 5.56mm Assault Ammo. And a 7.68x9.90 Rubber Pellet rounds with electron shocks in it. capable of stunning opponents and then switch back to lethal with a tap of a switch. The weapon is also modified for CQC variants; engraved spots on the rifle including stock, barrel, and grip mounts for combat knives.