SIG Sauer MCX Rattler Canebrake .300 BLK AR Pistol, 5.5 in Threaded Barrel, Coyote Tan
The MCX Rattler Canebrake is a compact .300 AAC Blackout AR pistol built around a purpose-built, suppressor-centric configuration. It features an SD-length free-float M-LOK handguard and a factory inert forward training device, plus a short-stroke gas piston system with adjustable gas settings. A 5.5 in carbon-steel barrel with 1:5 twist and 5/8x24 threads, a coyote tan Cerakote-finished receiver, and a side-folding SIG PCB-style brace round out a highly capable package that stays true to the Canebrake design.
Condition
Overall Condition: Very good condition, showing only light, superficial signs of prior handling or use.
Bore Condition: Excellent - Clean, mirror finish, no signs of wear.
Bore Rifling: Excellent Rifling - Sharp lands and grooves.
Specific Condition Notes: There are some minor scratches and blemishes present. The bore is clean and shiny.
What's Included
- SIG Sauer SIG MCX Rattler operator's manual
- One 30-round Magpul PMAG GEN M3 magazine for .300 BLK (marked 'AR 300 B')
This Canebrake configuration uses an SD-length free-float aluminum M-LOK handguard that extends forward over a factory inert training device, giving the model its distinctive profile and balance. The top is a full-length Picatinny rail for accessories, and the handguard integrates an anti-rotation QD sling socket.
The 5.5 in carbon-steel barrel is cut with a fast 1:5 twist to stabilize heavy .300 BLK projectiles and is threaded 5/8x24. The short-stroke gas piston system features adjustable gas settings tailored to .300 BLK performance. An ejection-port dust cover is fitted, and the design omits a forward assist by intent.
Controls are straightforward and modern, with an ambidextrous safety selector, a standard magazine release, and a curved trigger shoe. The rear of the receiver uses a 1913 rail interface to mount the side-folding, single-strut SIG PCB-style brace, finished in coyote tan to match the pistol's overall look.
The aluminum-alloy receiver wears a durable coyote tan Cerakote E190 finish. A SIG-branded textured polymer pistol grip offers a secure hold. The platform feeds from AR-15 pattern magazines and ships with a 30-round .300 BLK PMAG, providing a 30+1 capacity. Receiver markings include "SIG MCX – MULTI-CALIBER" and "SIG SAUER INC., NEWINGTON NH USA."