Primary Weapons Systems Enhanced Buffer Tube, Fits AR-15, Mil-Spec Receiver Extension, 6 Position, Ambidextrous Push Button Sling Points, Black, Includes Ratcheting Lock Castle Nut and Endplate 4G2BTMB-1F 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.