Get your new complete upper from Gunprime, the best source for your gun and ammo needs!! Through hard use in competition and in the woods and prairies of America Bushmaster has PROVEN itself above all other MSRs. Driven by the spirit of innovation that began more than 38 years ago using improved engineering manufacturing techniques and advanced materials at its new facility in Huntsville Bushmaster continues to enhance the ever-versatile MSR platform and many others. The AR in AR-15 stands for ArmaLite rifle the company that developed the design in the 1950s.