Striker Fire Excellence. The Sig Sauer P320 is a modular, striker driven platform that is arguably the most adaptable pistol design ever devised. A removable stainless steel Fire Control Unit (FCU) is easily removable and completely interchangeable with four different popular calibers. In addition, four different interchangeable frame size are available for the P320 series. The FCU itself is the serialized component will literally allow you to convert a 9mm sub-compact into a full-size .45ACP in a matter of seconds-- all without having to fill out another ATF 4473 form to buy a new handgun. For those who wish to maintain the consistency of a familiar weapons platform, but are look Mfg: Smith & Wesson