The Sig Sauer P320 is a striker-fired pistol chambered in 9mm, .40 S&W, .357 SIG, or .45 ACP. Its modular chassis lets users swap grip sizes, slide lengths, and calibers without tools, making it one of the more configurable pistols available. The polymer frame keeps weight down, the stainless steel slide provides durability, and the flat-faced trigger has a short reset. It comes in full-size, compact, and subcompact variants, and most models ship with an optics-ready slide.