SIG Sauer P320 Custom Works FCU 9mm — TiN-Coated Threaded Barrel, Window-Cut Slide, ROMEO1Pro Optic, 21-Round Mag
This full-size P320 Custom Works pistol combines SIG’s modular fire-control unit with a TiN-coated threaded barrel, window-cut long slide, and factory-installed ROMEO1Pro reflex sight. A flared magwell, aggressive stippled grip, and flat TiN trigger round out a competition-ready package that still accepts standard P320 magazines and accessories.
Condition
Overall Condition: Good condition, showing some signs of prior use and handling.
Bore Condition: Excellent – clean, mirror finish, no signs of wear.
The ROMEO1Pro optic is currently inoperable because the battery cap is damaged and cannot be removed. The front sight post is missing, and the slide shows finish wear, scratches, and visible tool marks from sight removal.
What’s Included
- SIG Sauer ROMEO1Pro open-emitter reflex sight (installed)
- 5.6-inch TiN-coated threaded barrel with knurled thread protector (installed)
- SIG Custom Works long slide with window cuts (installed)
- One factory 21-round steel magazine with extended polymer base pad
The heart of this build is SIG’s titanium-nitride–finished Fire-Control Unit, serialized with the “FCU” prefix that marks Custom Works production. This self-contained unit lets you swap slides, barrels, and grip modules while keeping the same serialized core.
Up top, the long slide carries wide front and rear cocking serrations for easy manipulation and weight-reducing window cuts that quicken the reciprocating mass. Its FDE/bronze Cerakote finish matches the TiN barrel for a cohesive look.
The 5.6-inch stainless barrel wears a durable TiN coating and 1/2-28 threads for a suppressor or compensator. A knurled protector keeps the threads safe when no device is installed.
Controls are competition-oriented: a flat, skeletonized TiN trigger delivers a straight-back press, the mag release is reversible, and a bilateral slide-catch lever accommodates either hand. The flared magwell speeds reloads with the included 21-round magazine.
The ROMEO1Pro red-dot sight is mounted directly to the slide for a low profile and fast sight picture. (See condition notes regarding its current inoperable state.) Suppressor-height iron sights co-witness through the optic window; only the rear sight remains installed.