SIG P320 Parts & Upgrades – Compare Prices

Last updated and checked October 28, 2026 · By Nick Hall

The SIG P320 is the most customizable handgun on the market, and it’s not particularly close. The entire gun is built around a modular fire control unit (FCU) that pops in and out of different grip modules, slides, and barrel configurations. One serial number, infinite builds. Want a full-size range gun on Monday and a compact carry gun on Friday? Same FCU, different parts. No other pistol does this.

We compare SIG P320 parts from Brownells, Palmetto State Armory, MidwayUSA, Optics Planet, and 200+ other retailers so you can find the best price on grip modules, slides, barrels, triggers, and everything else. Filter by part type, brand, and price. Every link goes straight to the retailer.

SIG built the Army’s M17 and M18 service pistols on the P320 (our SIG P320 review covers the gun itself), which won the Modular Handgun System contract. That means parts availability and aftermarket support are going to stay strong for decades. If you’re investing in this platform, you’re investing in something with a long future.

Table of Contents

Why the P320 Is the Most Customizable Handgun You Can Buy

Every other pistol on the market treats the frame as the firearm. Want a different size? Buy a different gun. Want a different caliber? Buy a different gun. The P320 threw that out the window. The fire control unit (the chassis that holds the trigger group) is the serialized firearm. The grip module, slide, and barrel are just parts, and federal law lets them ship to your door, though check your state before you order.

I’ve built three completely different P320 configurations from a single FCU. A full-size with an X-series slide and Wilson Combat grip for the range. A compact X-Carry setup for everyday carry. And an X-Compact with the 3.6″ barrel for deep concealment when I need it. One serial number in the safe, three different guns depending on the day.

The military adoption as the M17 (full-size) and M18 (compact) means this platform isn’t going anywhere. SIG and the aftermarket are heavily invested, and parts availability keeps getting better. It’s the closest thing the pistol world has to the AR-15’s ecosystem.

SIG P320 Fire Control Unit (FCU): The Heart of the System

The FCU is where every P320 build starts. It’s the stainless steel chassis that houses the trigger, sear, safety mechanisms, and the serial number, which SIG stamps on it as FCU followed by six digits. This is the only part of the P320 that legally constitutes a “firearm” and requires an FFL transfer.

The standalone FCU SIG sells today is the Custom Works unit, listed at $359.99 on SIG’s site. On October 28 our feed had it at $349.99 at Brownells. If you’re building a P320 from scratch rather than buying a complete gun and swapping parts, buying a standalone FCU and adding the components you want is the most efficient approach. You get exactly the configuration you want without paying for a complete gun’s worth of parts you’re going to replace anyway.

SIG Sauer lists its FCU as compatible with all 9mm, .357 SIG and .40 S&W parts. Drop the same FCU into a full-size grip module with a 4.7″ slide or an X-Compact grip with a 3.6″ slide. It doesn’t care. The .45 ACP P320 needs a different FCU, and the 10mm XTEN takes only .45 and 10mm parts, so neither mixes with the standard 9mm/.40/.357 lineup.

P320 Grip Modules: The Biggest Upgrade You Can Make

The grip module is where the P320 really shines as a customizable platform. Swapping grip modules changes the size, feel, weight, and ergonomics of the entire gun. And it takes no tools: rotate the takedown lever, lift the FCU out, drop it into the new grip.

Standard polymer grip modules come in Full-size, Carry and Compact, with XFull, XCarry and XCompact in the X-series. SIG lists the standard modules at $39.99 to $69.99 and the X-series at $89.99. The X-series grips have a higher undercut on the trigger guard, a flat-bottomed magwell, and a more aggressive texture. They’re a noticeable improvement over the original smooth grips, and retailers undercut SIG: an X-Series Compact module was $43.97 at Sportsman’s Outdoor Superstore on October 28.

The Wilson Combat grip module is one of the best-value upgrades you can make on a P320. Wilson lists it at $69.95, and the Carry version was $66.99 at PSA on October 28. The stippling pattern is aggressive without being uncomfortable, and the undercut is deeper than factory. It turns a good gun into a great one. I’ve put Wilson Combat grips on two of my P320 builds and have zero desire to go back. Wilson makes it in five sizes, and only the Carry and Compact come with a manual safety option.

The AXG (Alloy X Grip) is SIG’s all-metal grip. It’s heavier, which soaks up recoil, and has a metal-frame feel that polymer can’t match. SIG doesn’t sell it as a standalone module on its own site, but retailers carry the AXG Carry module: $310.99 at PSA on October 28. The TXG is SIG’s tungsten-infused polymer grip, heavier still for competition shooters who want weight to tame muzzle rise. SIG lists it at $249.99, and the X-Carry version was $152.44 at MidwayUSA.

Slides and Barrels: Changing Your P320’s Personality

The slide and barrel determine the size, weight balance, and optics capability of your P320 build. SIG offers several factory options, and the aftermarket is growing fast.

Factory slide options: The standard P320 slides are reliable but lack an optic cut. The X-series slides are cut for SIG’s PRO footprint and take the ROMEO1PRO, which is annoying if you want to run a non-SIG optic. The 10mm XTEN takes a ROMEO2 or a Trijicon RMR with a sealing plate. The Pro-Cut slides have lightening cuts for reduced weight and faster cycling. The Legion slides are the premium factory option with refined serrations and an enhanced finish.

Aftermarket slides fix that. Grey Ghost Precision cuts its 9mm P320 slides for the Trijicon RMR, Leupold DeltaPoint Pro or SIG Romeo1/Romeo1Pro, and Brownells sells RMR-cut slides for the Full Size and Compact ($219.99 at Brownells on October 28). That means you can run a Trijicon RMR, Holosun 507C/407C, or any other RMR-pattern optic without adapter plates.

Barrel lengths follow the slide: 4.7″ for Full-size, 3.9″ for Compact and Carry, and 3.6″ for the X-Compact. Buy the barrel listed for your slide length. Threaded barrels are available for suppressor or compensator use. SIG’s factory threaded barrels are good, and Faxon makes excellent aftermarket options: a Faxon Match threaded Full Size barrel was $121.99 at GunMag Warehouse on October 28.

P320 Triggers and Small Parts

The stock P320 trigger is decent. The curved version is perfectly functional for a duty or carry gun. But swap in a flat-face trigger and the difference is immediately noticeable. The flat face gives you a more consistent pull because your finger contacts the trigger at the same point every time regardless of where on the trigger you place it.

SIG sells their own flat-face trigger as a factory upgrade. The Armory Craft dual-adjustable flat trigger is the aftermarket pick, listed at $89.75 by Armory Craft (on sale at $64.75 when I checked), with adjustable pre-travel and over-travel that lets you tune the trigger to your preference. Apex’s P320 flat trigger still turns up at retailers ($47.45 at Kentucky Gun Co on October 28), but Apex no longer lists a P320 trigger on its own site, so buy it while it’s stocked or plan on the Armory Craft.

For small parts, the P320 is low-maintenance. SIG’s manual treats the recoil spring assembly as one unit you service as a whole and says to clean and lube at least every 500 rounds; it gives no round count for replacing springs. SIG OEM replacement parts are affordable and easy to find. Keep a spare recoil spring assembly on hand if you shoot regularly.

Caliber Conversion Kits: One Gun, Multiple Calibers

This is one of the P320’s most underappreciated features. Because the FCU covers 9mm, .357 SIG and .40 S&W, you change caliber without touching the serialized part.

.40 S&W and .357 SIG: These two share magazines. SIG sells its P320 .40/.357 SIG magazines with one label covering both (14, 13, 10 and 18 rounds), because .357 SIG is a .40 S&W case necked down. 9mm magazines are their own thing.

9mm to .40 S&W or .357 SIG: SIG’s Caliber X-Change kit is the clean path. The 9mm to .40 kit comes with the slide, barrel, recoil spring, a 10-round magazine and a grip module, and you keep your FCU. SIG lists the kits at $599.99 to $799.99, and a .357 SIG Compact kit was $415.99 at Brownells on October 28.

.45 ACP and 10mm: This is the big exception. The P320 in .45 ACP needs its own FCU, and the 10mm XTEN takes only .45 and 10mm parts. Neither interchanges with the 9mm/.40/.357 family, so a .45 or 10mm P320 is essentially a separate gun.

Caliber conversion kits are the easiest way to convert. SIG and several aftermarket manufacturers sell them. Use the price comparison grid above to find the best deal on conversion kits across 200+ retailers.

P320 Magazines: Capacity and Compatibility

P320 9mm magazines come in four standard capacities: 12-round (Subcompact), 15-round (Compact), 17-round (Full-size) and 21-round extended. SIG lists each standard magazine for its own size only, so buy the one that matches your grip module. On October 28 a SIG 17-round was $39.99 and a 21-round $43.99, both at GunMag Warehouse.

SIG says its magazines come from more than one manufacturer, built to SIG’s own specifications. Stick with SIG-branded or SIG-listed magazines for a carry gun, and test any other magazine at the range before you trust it.

For states with magazine capacity restrictions, SIG sells 10-round versions. The 21-round extended magazines are great for range use and competition, and the grip extension gives your pinky somewhere to live.

How to Buy P320 Parts Smart

The P320 parts market has a wide price spread depending on where you shop. SIG’s own website sits at list price, and retailers often come in under it: the FCU was $359.99 at SIG and $349.99 at Brownells, and the Wilson Combat module $69.95 at Wilson and $66.99 at PSA. Brownells, Palmetto State Armory, and MidwayUSA are the first three stores to check for grip modules, magazines, and small parts.

For FCUs and complete slide assemblies, SIG OEM is the right call. The engineering tolerances on the FCU matter, and SIG’s quality control on their own parts is excellent. For grip modules, the Wilson Combat option is better than anything SIG sells at that price point. For triggers, the Armory Craft beats factory.

Watch for P320 “parts kit” bundles that include a slide, barrel, recoil spring, and grip module as a package. These sometimes offer better value than buying each component individually. Use the price comparison grid above to check current pricing across all 200+ retailers before you buy anything. For our picks by category, see the best SIG P320 parts and accessories; if your gun is acting up, start with common P320 problems; and for anything outside the P320, run a gun price check.

Facts and Figures

• The FCU is the serialized part of a P320; SIG lists it as compatible with all 9mm, .357 SIG and .40 S&W parts.
• .40 S&W and .357 SIG share P320 magazines; 9mm magazines are separate.
• The .45 ACP P320 needs its own FCU, and the 10mm XTEN takes only .45 and 10mm parts.
• P320 9mm magazines hold 12 (Subcompact), 15 (Compact), 17 (Full-size) or 21 (extended) rounds.
• Barrel lengths: 4.7 in Full-size, 3.9 in Compact and Carry, 3.6 in X-Compact.
• On October 28, 2026, a SIG Custom Works FCU was $349.99 at Brownells in our feed.

Frequently Asked Questions