The Pneumatic Valve and Rod system was created to be a more reliable alternative to the Stoner bolt and carrier piston system used in the AR-15 family, commonly but incorrectly referred to as a
direct impingement system. UDMC states that the PVAR system is designed to be easily removed from the front of the gas block, and does not require removal of the handguard to access the gas system for cleaning or repairs. The PVAR system was designed in an attempt to reduce malfunctions by preventing the buildup of heat, lead and copper fouling inside the receiver by utilizing mechanical energy instead of the pressurized gases of the cartridge to cycle the bolt, the process by which a round of ammunition is fired, ejected, and a new round is loaded. Instead of a hollow gas tube, it uses a one piece bolt carrier with a piston rod which transfers the energy of the gas produced by the round and pushes the bolt carrier rearwards. The manufacturer advertises that the PVAR system reduces the need for field maintenance and overall wear and tear compared to the standard AR-15 design. Unlike many gas piston systems, the PVAR features a free-floating piston rod that, upon firing, travels rearward and essentially increases the mass of the bolt carrier group during most of the firing cycle in order to reduce recoil. The manufacturer states that this system is compatible with barrel twists of 1:7, 1:9, and 1:12, as well as M193 and M855 ammunition. Compared to a standard AR-15, the PVAS rifle has a slower rate of fire of around 750rpm due to the increased effective mass of the bolt carrier group when firing. The bolt head is milled from
Carpenter 158 steel and the Bolt Carrier Groups are made of AISI 8620 steel. == Users ==