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. The 13.5×1 LH piston allows the use of PWS suppressors on 13.5×1 LH threads.