Modular Guns: Assembling a SIG USW-320

Today I’m at SIG Sauer Parts (soon to be ModGuns) to play around with assembling a SIG 320. I’ve always been interested in stocked pistols, and so I’m going to take this opportunity to put together a USW (Universal Service Weapon). This originated as a complete pistol made by B&T (based on the CZ75) with an integrated folding stock and Aimpoint Nano optic. B&T decided to also make stocked chassis units for Glock and SIG pistols, and so the SIG model is what I’ll do doing today. The modular design of the SIG 320 should make this a fun and pretty simple process…


  1. Thanks! This is one of the most comprehensive assembly videos I’ve seen, the only one in a league with MCARBO’s.

    The USW is a rare exception to the P320’s unfulfilled potential. SIG seems to divide its time equally between advertising modularity, decommissioning the product lines that offered real versatility, and introducing minor cosmetic variations of the week. Frankly, the P365 has more potential for versatility, and I hope the “Macro” enjoys enough success for them to capitalize on it.

    The fact that the chassis includes the FCG (among the first factory parts most customizers replace) is just the icing on the cake.

  2. Nobody watching this has ever assembled anything whilst drunk, angry, or worried: apart from me; who wishes I’d been as calm and focused when I tried to put things together.

  3. Did you scratch your form 1 info on the FCG where it can’t be seen in the assembled form or did you put that on an external part?

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