The concept of a steel chassis, or Fire Control Unit (FCU), containing the functional parts of a pistol within a polymer frame was not new when Sig released the P320 and P365. But taking advantage of that chassis being the serialized part and building a wealth of aftermarket options is. This is exactly what the SIG Sauer Custom Works FCU Studio does.

SIG Sauer Custom Works Studio P365

Not only has Sig Sauer fostered aftermarket options, but they’ve made plenty slide and frame options of their own. Now, with Sig’s Concierge Service and Custom Shop, you can order the specific combination of frame, slide, and barrel you want and have it built for you.

Options for the 365 and 365XL are understandably less than the ubiquitous 320 series. But there are still plenty of options. For the 365 the list can be found in the Custom Works Studio. Here you can select your Grip Mod, Slide, Barrel, Guides & Springs, Magazines, and Optics. As a result, you can visualize the build to your taste.

Note that parts orders through the Custom Works P365 Studio don’t currently include the FCU needed for a complete firearm.

There may be some lead time as Sig gathers the parts and builds your firearm, but in today’s market wait time is the name of the game. Wouldn’t you rather wait for the exact build you want than wait for whatever arrives at the local gun store?

Using the SIG Sauer Custom Works FCU Studio

As of the time this article was written, between the P365 and P365XL there are six frame options, seven slide options, standard barrels, recoil assemblies, nine magazine options, and two optics options.

The availability of affordable replacement grip frames also makes home stippling attempts a little less intimidating. Unlike a traditional pistol, a botched stippling attempt doesn’t destroy the firearm with the Sig FCU system.

The Sig Custom Works site is clever enough to prevent combining parts that won’t work as a complete firearm. Likewise, it even verifies magazine capacity legal compliance via your zip code.

All of it is professionally assembled and packaged by Sig Sauer just as they would a common production gun. But the Titanium-nitride coated Sig Custom Works fire control unit confirms this was not another home-built project.

When our build is complete and in hand, we’ll have a full review in an upcoming issue of Personal Defense World magazine. It will outline our choices and experience with the Concierge service, why we chose the build we did, and how it performs on the range. How would you build out your P365 or P365XL?

For more information, please visit

The SIG Sauer Custom Works FCU.

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