The modular P320 allows you to select any of several centerfire calibers. Just disassemble the pistol and reassemble it with the X-Change Kit’s barrel/slide assembly, grip module, and 17 round magazine. Not compatible with manual safety models of the P320. This kit features SIG SAUER’s exclusive side-mounted optic, the ROMEO1 pre-zeroed, which ensures faster sight acquisition on target.Note: CALX kit comes with contrast sights.