Sig Sauer MCX Rattler PCB .300 AAC Blackout AR Pistol, Short-Stroke Gas Piston, Side-Folding PCB Brace, Threaded Barrel, Matte Black
This is an original pre-LT MCX Rattler PCB in .300 AAC Blackout, configured with Sig's internal recoil system for a true side-folding brace and a compact, duty-focused layout. It features an adjustable gas regulator accessible through the handguard, a short free-float M-LOK handguard with relief windows, and a full-length Picatinny top rail. It comes in excellent overall condition with an included Magpul PMAG Gen M3 300 BLK magazine.
Condition
Overall Condition: Excellent condition, showing only faint signs of any prior use or handling.
Specific Condition Notes: Displays minimal evidence of prior handling and firing, with only light wear visible on close inspection.
Bore Overall Condition: Excellent - Clean, mirror finish, no signs of wear.
Bore Rifling: Excellent Rifling - Sharp lands and grooves.
What’s Included
- Sig Sauer MCX Rattler PCB .300 AAC Blackout pistol
- 1x 30-round Magpul PMAG Gen M3 for 300 BLK (polymer) with "7.62x35 / 300 BLK" markings
This Rattler is the original pre-LT PCB configuration, built around Sig Sauer’s short-stroke gas piston system and internal recoil assembly. The design eliminates the need for a buffer tube, allowing a true side-folding PCB brace for a compact footprint without compromising function.
The PCB brace uses a Velcro strap and folds to the side for storage and transport. Controls are modern and ambidextrous, including the safety selector and charging handle with bilateral latches, while the pistol retains a straightforward curved trigger and an AR-pattern polymer grip.
The aluminum free-float M-LOK handguard is short for maneuverability and features large relief windows. A full-length Picatinny top rail runs from receiver through the handguard. The adjustable gas regulator, marked with plus/minus icons and accessible through the handguard, supports tuning for varying ammunition or use conditions. The barrel is threaded at the muzzle.
Receivers are aluminum alloy with a hard-anodized matte black finish. Factory markings read "SIG SAUER INC NEWINGTON NH USA," and the pistol is made in the USA. The platform’s relevance is underscored by USSOCOM’s published intent in 2022 to procure MCX Rattlers for its PDW program. This example ships without sights and includes a correct 300 BLK Magpul PMAG Gen M3 magazine.