The SIG Sauer P320 Fire Control Unit (SIG part no. 8900161) is the serialized heart of the modular P320 system — the actual firearm in a P320 build, since every grip module, slide, and barrel is built around this single chassis. SIG ships this fire control unit stripped, in black, without a thumb safety, so builders can drop it into whichever grip module and caliber configuration they want to run. Because the fire control unit itself carries no fixed caliber, it can move between 9mm, .40 S&W, and .357 SIG builds simply by swapping the grip module, slide, and barrel around it. Shooters building or expanding a modular P320 system start here, since this is the one component that legally defines the pistol.

Key Specifications

• Functions as the serialized fire control unit — the legal firearm in any P320 build.
• Ships in a stripped configuration for builders assembling their own P320.
• Finished in black.
• Built with no thumb safety, matching SIG’s standard P320 trigger configuration.
• Operates as a semi-automatic action.
• Not tied to a single caliber, supporting 9mm, .40 S&W, and .357 SIG configurations depending on the grip module, slide, and barrel installed.
• Weighs approximately 0.6 pounds bare.
• Classified by the manufacturer as a Striker Fired fire control unit.

Frequently Asked Questions

Is this the actual firearm, or just a part? This fire control unit is the serialized component — it’s the legal firearm in a P320 build, regardless of which grip module surrounds it.

Does it include a thumb safety? No, it’s built without a thumb safety.

What calibers can this run? 9mm, .40 S&W, and .357 SIG, depending on the slide, barrel, and grip module you pair with it.

Buy the SIG Sauer P320 Fire Control Unit

Start or expand your modular build with this SIG Sauer fire control unit. Browse more in our handgun frames selection. As a serialized firearm, it ships to your FFL from our Lubbock, Texas gun shop.