SIG Sauer MCX Rattler PSB .300 AAC Blackout AR Pistol, 5.5 in Threaded Barrel, Side-Folding Brace, ROMEO-MSR Red Dot
The SIG Sauer MCX Rattler PSB in .300 AAC Blackout delivers a compact, piston-driven AR pistol with a 5.5 inch threaded barrel, bufferless receiver, and a side-folding brace for minimal overall length. This example includes a factory-installed SIG Sauer ROMEO-MSR red dot and a 30-round PMAG marked for 300 BLK. The platform’s PDW pedigree is underscored by its selection by U.S. SOCOM for the PDW/RSAR program in 2022.
Condition
Overall Condition: Very good condition, showing only light, superficial signs of prior handling or use.
Specific Condition Details: This firearm is in great shape. There are some minor and superficial scratches and blemishes present.
Bore Overall Condition: Excellent - Clean, mirror finish, no signs of wear.
Bore Rifling: Excellent Rifling - Sharp lands and grooves.
What’s Included
- Plano hard case
- SIG Sauer ROMEO-MSR red dot sight (installed)
- 1x 30-round Magpul PMAG for 300 BLK (marked 7.62x35/300 BLK)
The MCX Rattler’s short-stroke gas piston system and rotating bolt provide reliable function in a compact package optimized for .300 BLK. Its bufferless receiver with a 1913 rear interface allows the brace to fold to the left, enhancing portability without changing the pistol’s operating system.
The 5.5 inch carbon steel barrel is threaded and fitted with a factory three-prong flash hider. Up front, a short free-float aluminum M-LOK handguard offers slots at 3, 6, and 9 o’clock, an integrated QD socket, and a full-length 1913 top rail for mounting accessories.
Controls are well laid out, with an ambidextrous safety selector and ambidextrous bolt catch/release, plus a right-side magazine release. The included SIG Sauer ROMEO-MSR 1x red dot with a red dot reticle is installed, and there are no iron sights on this setup.
The aluminum alloy receivers feature a hard-coat anodized finish for durability. With a stated capacity of 30+1 and a brace equipped with a Velcro strap, this PSB configuration is purpose-built for the MCX Rattler’s PDW role, a role highlighted by the platform’s selection by U.S. SOCOM in 2022.