The SIG516 is a semi-automatic multi-caliber rifle. It fires from a closed bolt, and has a short-stroke push rod piston system. The gas piston pushes the bolt carrier rearward, where it is returned to the forward and locked position by a spring. This process loads the next cartridge. The 516 has a four-position gas regulator, allowing the user to choose the amount of gas directed to the piston.
