Up for sale is a Pre-Owned SIG MCX Rattler 5.5” complete upper receiver chambered in .300 Blackout—built for serious performance in an ultra-compact package. Designed around SIG’s proven short-stroke piston system, the Rattler delivers exceptional reliability, reduced recoil, and cleaner operation compared to traditional direct impingement setups.
This upper is purpose-built for close-quarters efficiency, making it an ideal choice for suppressed shooting, home defense, or a compact truck setup. The SIG MCX Rattler 5.5” barrel maximizes the .300 Blackout platform’s strengths, offering impressive energy and performance even in a short configuration.
Condition:
Complete and ready to drop onto your lower, this Sig MCX Rattler upper is a premium option for anyone looking to upgrade with one of the most sought-after compact .300 Blackout systems on the market.
