The term operating system generally refers to the method by which a firearm loads a cartridge into a breach and ejects the round after the shot is fired. Operating systems mostly refer to semi-automatic or automatic firearms—so-called “autoloading” firearms. Types of operating systems include recoil operation—typical to modern striker-fired handguns like the SIG SAUER P320—gas operation like that of a typical AR-15, and subsets of gas operation like gas piston (which is the operating system on SIG SAUER MCX Virtus rifle) and gas impingement.