SIG Sauer MCX Rattler SBR 5.56 NATO, 7.75 in, Short-Stroke Piston, Folding Stock, ROMEO5XDR + JULIET5 Micro
This SIG Sauer MCX Rattler SBR is a compact, piston-driven 5.56 NATO variant with a 7.75 in barrel, a side-folding stock, and a two-position adjustable gas regulator. It comes outfitted with a Midwest Industries 9.8-inch M-LOK handguard and includes a SIG SAUER ROMEO5XDR red dot and JULIET5 Micro flip-to-side magnifier. The muzzle brake incorporates a QD-style suppressor mount, and the rifle carries factory MCX Rattler markings along with custom trust engraving.
Condition
Overall Condition: Very good condition, showing only light, superficial signs of prior handling or use.
Bore Overall Condition: Excellent - Clean, mirror finish, no signs of wear.
Bore Rifling: Excellent Rifling - Sharp lands and grooves.
Specific Condition Notes: The firearm presents in great shape with minor scratches and blemishes consistent with light handling.
What’s Included
- Midwest Industries (MI) 9.8-inch M-LOK handguard (installed)
- SIG factory pistol grip (installed)
- SIG SAUER ROMEO5XDR red dot sight
- SIG SAUER JULIET5 Micro flip-to-side magnifier
- Vertical foregrip (installed)
- 1x 30-round USGI-pattern metal magazine marked '5.56 mm x 45'
The MCX Rattler SBR architecture centers on SIG's short-stroke gas piston system and a very short 7.75 in barrel, giving this rifle fast, reliable cycling in a compact footprint. A two-position adjustable gas regulator with clearly marked +/- settings supports tuning for different setups, and the three-chamber muzzle brake incorporates a QD-style suppressor collar.
The skeletonized side-folding stock on the MCX hinge locks up solidly while keeping weight low and storage simple; its rubberized buttpad and 12.5 in length of pull add control in a small package. Controls are well-sorted, with an ambidextrous safety featuring pictograms on both sides, AR-style bolt catch and magazine release, and an ejection-port dust cover. The receivers are aluminum.
Up front, a Midwest Industries 9.8-inch free-floating aluminum M-LOK handguard is installed, featuring elongated M-LOK slots and a short 12 o'clock 1913 Picatinny section at the rear that mates to the receiver; the forward 12 o'clock is open and does not form a continuous full-length top rail. A vertical foregrip is installed for added purchase and control.
This rifle includes a SIG SAUER ROMEO5XDR red dot sight paired with a SIG SAUER JULIET5 Micro flip-to-side magnifier, giving rapid target acquisition with optional magnification. Factory markings include the right lower marked "SIG SAUER INC NEWINGTON NH USA," the upper marked "RATTLER," and the left magwell with the circular SIG logo and "SIG MCX MULTI-CALIBER." Custom trust information is engraved within the trigger guard, with additional text "DANIEL MCGREGOR MAYER / PITTSBURGH, PA."