This polymer lower for the SIG Sauer P320 is designed to transform a full-size or compact pistol into a B&T USW-320 complete with integrated stock. All you need to do is transfer the trigger group, slide, and magazine release onto the new unit. The USW-320 mirrors the full-size P320’s footprint so 17-round (and bigger) magazines can be used. The company claims that with the integrated stock (which may also be folded away) accuracy and effective range can both be significantly improved.