The Mark 12 Mod 0 SPR Upper Receiver from Precision Reflex is a complete, fully tricked out tactical upper that's ready to attach to the lower of your choice and deliver MOA accuracy. The key to the Mod 0's impressive accuracy is the free-floated, 18" Douglas barrel of high-grade 416 stainless steel with 1-7" target rifling and M4-type feed ramps. The bolt is custom-fitted to the barrel. The core of the PRI Mark 12 Mod 0 SPR Upper Receiver is a mil-spec forged AR-15 flattop receiver with a standard commercial carrier, so compatibility with a mil-spec (.250" pivot/takedown) lower is no problem. Popular tactical/competition features: Rifle-length gas Mfg: Precision Reflex