Primary Weapons Systems MK1 Mod 2-M, Complete Lower Receiver, Semi-automatic, 556NATO, Magpul Furniture, Hard Coat Anodized, Black, 30 Rounds, All Proprietary Ambi Parts Included MK1-M2-LWR-CR 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 ambidextrous MK1 MOD 2-M Multi-Caliber Lower, T6 7075 Forged, Anodized, AR-15 Compatible.