Many years ago, I picked up a SIG Sauer P250 in .45 ACP. At the time, as a resident of Massachusetts subject to the vagaries of the "Approved Handgun Roster," it was the only compact, polymer-frame .45 ACP available. The modular nature intrigued me, and I picked up a sub-compact frame, slide and barrel to investigate as well.
Flash forward to the introduction of the P320, and the same modular assembly-system is in use for the striker-fired variant. Sure enough, SIG was clever enough to offer the same mix of frames, slides and barrels for the P320 as they did for the P250; in fact, the frames are interchangeable. Owing to geometry in the slide with regard to striker vs. hammer, the X-Change kits themselves are not interchangeable between the P250 and P320, however.
The Caliber X-Change Kit shown changes a compact or sub-compact P250 of any caliber into a full-size pistol. Whether a 6-round, .45 ACP sub-compact or a 13-round, .40 S&W compact model, with this kit it transforms into a 17-round handgun suitable for competition, duty or just higher-capacity daily carry.