SIG SAUER P320

Overview

The P320 is a striker-fired, polymer-frame pistol family from SIG Sauer introduced in the mid-2010s. Its standout feature is a **modular fire-control unit (FCU)** - the serialized chassis - which lets you change frame sizes, slides, and calibers without buying a whole new gun.* **Modular FCU (fire control unit)** - serialized part; swap chassis between grip modules and slide assemblies to change size/caliber.* **Striker-fired action** with multiple trigger variants (stock, X-Series flat trigger, and aftermarket upgrades).* **Interchangeable grip modules** (Full, Carry, Compact, Subcompact, X-Series ergonomics).* **Calibers** commonly produced: 9mm (most common), .40 S&W, .357 SIG (less common), .45 ACP (X-Full/X-Compact conversions possible with the right slide/barrel/kit).* **Accessory rail** on most full/compact slides for lights/lasers.* **Optics-ready models** (RX, XSeries RX) or slides with removable cover plates to mount red dots (footprint depends on slide/plate).# Common variants (overview)* **P320 Full / Carry / Compact / Subcompact** - size/slide length differences for carry vs duty vs competition.* **P320 XSeries (XCarry, XCompact, XFull, XFive Legion, etc.)** - upgraded ergonomics, improved triggers, extended controls, often marketed for competition and carry.* **P320 RX / optics-ready models** - sold with milled slides or cover plates for mounting red dot optics; sometimes bundled as "X Combo" with a SIG red dot.* **P320 M17 / M18** - military contract variants (M17 is full size, M18 is carry-size) with specific features. **Concealed carry**: Carry/Compact/Subcompact grip + short slide.* **Duty / home defense**: Full/XFull with higher capacity mags and longer sight radius.* **Competition**: XSeries and optics-ready slides; aftermarket triggers and barrels.* **Modular hobbyist**: switch FCU into different size modules for multiple roles.# Upgrades & accessories people commonly add* **Aftermarket triggers** (crisper pull, shorter reset) - many reputable makers.* **Optics**: ROMEO series, RMR, RMSc alternatives - confirm slide footprint or use optics-ready slide.* **Barrels**: threaded barrels for suppressors, match barrels for accuracy.* **Slides**: optics-ready or custom serrations, coatings.* **Holsters**: get one cut for the exact slide + optic combo.* **Sights**: suppressor-height sights for co-witness with red dots, night sights (tritium).(1)15+ RND MAGStreamlight TLR-7XSig Sauer Romeo 1 Pro