The Sig Sauer P320 FCU is the serialized fire control unit at the center of the P320's modular design, chambered here in .357 SIG with a Gold Nitride finish. The FCU itself is 6 inches long and weighs 1 lb, and it uses a flat face trigger. 
 

Key Specifications 

• Brand: Sig Sauer 
• Model Name: P320 
• Caliber: 357 SIG 
• Length: 6 inches 
• Weight: 1 lb 
• Grip Type: Standard 
• Trigger Type: Flat Face 
• Finish: Gold Nitride 
• Condition: New in Box 
   

Detailed Features 

 
The Gold Nitride finish is a hard surface treatment that improves wear and corrosion resistance while giving the unit a distinctive gold appearance. The flat face trigger geometry changes where the finger contacts the trigger face, which some shooters find improves consistency and the perceived pull weight. At 1 lb and 6 inches, this is the FCU alone -- the complete pistol requires a grip module and slide assembly. 
 
The P320's modularity means this FCU can be moved between different grip modules and slide configurations as needs or laws change.

Sentiment around the P320 FCU in .357 SIG is generally positive among P320 owners who appreciate the platform's modular design. The Gold Nitride finish draws collectors and shooters who want something visually distinct. The .357 SIG caliber gets praise for velocity and terminal performance, though discussions frequently note that ammunition is harder to find and more expensive than 9mm.

The grip can feel bulky for smaller hands, which is a recurring comment. Overall, buyers who understand they're purchasing the FCU component -- not a complete pistol -- tend to be satisfied with the build quality and the versatility the modularity provides.