an Entity references as follows:
UDMC PVAR rifles are Filipino variants of the Armalite AR-15 and AR-10 using the Pneumatic Valve and Rod system manufactured by United Defense Manufacturing Corporation. 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.