Primary Weapons Systems was formed by firearm enthusiasts in 2008. Starting out by producing muzzle devices, they tested their compensators on all different types of rifles - from M4s to AK-47s. After using both styles of rifles in testing with high round counts, the difference in maintenance needed was both astounding. From that basic realization, the PWS long-stroke piston system was born; keeping the core values of the AR-15 design, while also lessening the need for maintenance in high-volume fire situations and adverse conditions. PWS MK1 MOD 2-M Multi-Caliber Lower, T6 7075 Forged, Hard Coat Black Anodized per MIL-A-8625F Type III Class 2, AR-15 Compatible. Proprietary Parts Included: Left side magazine release, Bolt catch spring, Bolt catch screws, Tension screw, Bolt release lever, Bolt release through pin