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 Compound Rifle is a combination of a Mod 1 upper, with the Mk1 Mod 2 Lower.Features :Operating System: PWS Long Stroke Piston System, 3 setting Adjustable Gas RegulatorCaliber: .223 Wylde,Barrel Length: 16.1";"Gas System Length: Mid-Length,Barrel Twist Rate: 1:8Muzzle Velocity: 2980fpsMuzzle Device: PWS FSC 556Upper Receiver: PWS Proprietary Piston Upper, T6 7075 Forged, Anodized,Handguard: PWS M-Lok 15.05" Handguard (1.7" width, 2.25" height),Charging Handle: Radian Raptor Ambidextrous Charging Handle