SIG SAUER® Compatible Build Kit

Sig Sauer's modular P320 handgun made waves since its introduction in 2014, earning favor with the U.S. Military and law enforcement agencies nationwide, designated the M17 and M18 Service Pistol. This unique platform allows you to easily convert your new pistol into a plethora of different profiles and calibers using a combination of parts.

Four Pistols, Three Calibers, One Gun

The Sig P320 converts between a full-size, carry, compact, and subcompact configuration. It offers chambers in 9mm, .357 SIG, and .40 S&W. The key to the P320's modular design is the singlular, universal chassis considered the firearm component in the platform. Called the Modular Universal Pistol (MUP-1) insert, this chassis ships to you directly as an "80% receiver" -- not yet functional, not considered a firearm. The chassis contains the bulk of the fire control group, including the lower parts kit, trigger assembly, and operating springs. It serves at the mounting platform for the interchangeable slides, barrels, frames, and magazines.

Creating a Build-Your-Own P320 Kit

Completing the 80% chassis turns it into a functional firearm by definition. Your chassis's fabrication requires basic hand tools, but no technical knowledge or gunsmithing experience.  Assembling your completed Sig chassis into a functional P320 requires purchasing a separate parts kit and the finishing jig. The jig shows you where and how to cut and drill the 80% blank. This visual instructional video details each step required for completing the chassis with the jig:

Building Your Sig P320: Federal and State Laws

The only component of the Sig Sauer P320 that's considered a firearm under federal is the fire control unit (FCU). But with the 80% P320 kit, the FCU is not fabricated. It cannot accept a trigger, slide, or other parts so the ATF does not consider it a firearm, nor does federal law. That means your unfinished 80% chassis ships directly to you without the need to visit an FFL, pay any transfer fees, fill out any paperwork, or conduct a federal background check. All other parts required to finish the chassis are sold separately.

Some states have banned 80% frames like the P320 80% FCU, and certain firearm parts, or have otherwise restricted the sale and ownership of products we sell. So, be sure to check your local and state laws. We can’t ship our products to certain states. Please check our Shipping & Return Policy before placing an order (see restrictions).

Your build awaits.

DISCLAIMER: If you are new to the world of DIY gun building, you likely have a lot of questions and rightfully so. It’s an area that has a lot of questions that, without the correct answers, could have some serious implications. At 80-lower.com, we are by no means providing this content on our website to serve as legal advice or legal counsel. We encourage each and every builder to perform their own research around their respective State laws as well as educating themselves on the Federal laws. When performing your own research, please be sure that you are getting your information from a reliable source.