The P516 is based off the SIG 516 rifle that is built on a AR-15-type platform with a refined operating system that is combat-reliable. The 516 series—both the rifle and the pistol—use a short-stroke, gas-piston/pushrod operating mechanism in place of the conventional direct-impingement gas system found on a normal AR-type platform. Carbon fouling and excessive heat are prevented from ever reaching the chamber or bolt carrier thanks to this piston mechanism. Upper and lower receivers of the P516 are made of forged 7075-T6 aluminum, and the upper receiver has a hard coat anodized finish. A free-floated, military-grade, nitride-treated 10-inch barrel with a twist rate of 1:7 inches and six grooves is featured on the top. There is an A2-style flash hider at the muzzle. Having enough gas to run the system when the AR-type platform's barrel length is reduced is an engineering challenge.