SIG SAUER® Compatible Build Kit

SIG SAUER® Compatible Build Kit

Sig Sauer's new P320 modular handgun platform has 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 that are not individually considered firearms under federal law. With a handgun that transforms in a matter of minutes using a single firearm chassis, it only makes sense that the new P320 got the 80% receiver treatment.

Four Pistols, Three Calibers, One Firearm by Definition

The Sig P320 easily converts between a full-size, carry, compact, and subcompact configuration, offering 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 slide, barrel, frame, and magazine.

Cutting and Fabricating the 80% Sig Chassis

Completing the chassis to make it a functional firearm by definition is incredibly simple, requiring only basic hand tools with no advanced knowledge or gunsmithing experience. This visual instructional video details each step required for completing the chassis:

What's Included With Your Kit

Modular Universal Pistol 1 (MUP1) insert: The basis of your P320 platform. This is the Fire Control Unit you’ll need to fabricate with the included jig. This process enables you to finish your P320 on your own without the need to go through an FFL.

The Chasis 80% Jig: Required to finish your MUP1 80% insert. It takes away the guesswork by showing you where to drill and what to fabricate. No experience necessary.

The lower parts kit: Required to assemble your FCU into a ready-to-fire insert.

The P320 “exoskeleton”: A factory slide with night sights (includes barrel and guide rod/recoil spring assembly) , a factory grip module (frame).

Carrying Case: A simple, convenient carrying case to protect your newly minted P320.

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 P320 build kit 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.

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, 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.

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We are a national retailer of individual components and not all products depicted on this website are legal in every state. Shipping of various products found on this website are prohibited to some states (such as California, Connecticut, District of Columbia, New Jersey, New York, Rhode Island, and Washington). The information, pictures, text or products presented on this website are not a representation by us, and should not be understood by you, that any product or completed firearm is legal to assemble or own in your state of residence. We encourage each and every builder to perform their own research about the state and federal laws that apply to them. It is your responsibility to understand the law and we encourage you to consult with an attorney or your local ATF representative.