Specifications and Features: American Tactical Imports ATIGLOW200. Reinforced polymer lower receiver. The weight of a polymer lower with the strength of a billet lower. Inter-lock hammer and trigger pin retainment system built into the lower. Prevents movement from the hammer and trigger pin during firing. Works with standard LPK. Marked Multi Cal. Black. The Omni Hybrid Multi-Cal AR-15 lower receiver is the perfect combination of strength and durability. Tested and rated to be as strong as a billet receiver the new design provides extra strength in the high pressure sections and is designed to surpass the military pressure and weight bearing testing. So build your next 5.56mm NATO .300 AAC Blackout or any one of the other popular AR-15 caliber conversions.