Sig Sauer MCX Rattler .300 AAC Blackout AR Pistol, 6.75 inch Barrel, 5/8x24 Threaded, Adjustable Gas, Folding SIG PCB Brace, Black
This Sig Sauer MCX Rattler stands out for its ultra-compact 6.75 inch .300 BLK configuration, short-stroke gas piston system, and two-position adjustable gas for suppressed or unsuppressed use. It features a folding SIG Pivoting Contour Brace on a 1913 rear rail, a free-floating PDW handguard with M-LOK slots and a full-length 1913 top rail, and a 5/8x24 threaded barrel with a three-prong flash hider. Marked with SIG factory roll marks and made in the USA, it includes both 30- and 20-round PMAG Gen M3 300 BLK magazines.
Condition
Overall Condition: Very good condition, showing only light, superficial signs of prior handling or use.
Specific Condition Notes: This firearm is in solid shape and shows some scratches and blemishes.
Bore Overall Condition: Excellent - Clean, mirror finish, no signs of wear.
Bore Rifling: Excellent Rifling - Sharp lands and grooves.
What’s Included
- 1x 30-round Magpul PMAG Gen M3 '300 BLK' polymer magazine
- 1x 20-round Magpul PMAG Gen M3 '300 BLK' polymer magazine
The MCX Rattler uses a semi-automatic, short-stroke gas piston system with an adjustable two-position gas setting optimized for suppressed or unsuppressed firing. Its .300 AAC Blackout chambering and 6.75 inch barrel deliver a compact PDW package built around reliability and control.
The barrel is threaded 5/8x24 and ships with a three-prong flash hider installed. A full-length 1913 top rail integrates with the free-floating PDW aluminum handguard, which includes M-LOK slots for mounting accessories. An ejection-port dust cover is present.
Controls are purpose-built: ambidextrous safety selector and ambidextrous charging handle, a left-side bolt catch, and AR-pattern magazine compatibility with an AR-pattern magazine release. The trigger is a curved profile.
At the rear, a 1913 rail hosts the SIG Pivoting Contour Brace (PCB), which folds for storage and transport. The receiver is aluminum alloy with a black hard-coat anodized finish, matching the black anodized aluminum handguard. Factory markings include "SIG SAUER INC NEWINGTON NH USA," a large SIG logo, "SIG MCX MULTI-CALIBER" on the receiver, and "RATTLER" on the upper. Made in the USA.