Sig Sauer MCX Rattler Upper Assembly - 5.5" 300blk

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MSRP: $1,799.00
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Frequently bought together:


Sig Sauer SIG MCX Rattler Upper 300 Blackout


  • 5.5" Barrel
  • M-Lok Handguard
  • Side Folding AR Buffer Tube Knuckler
  • Includes Charging Handle
  • Bolt Carrier
  • Sig Duo Matchlite Trigger
  • 1913 Adapter to convert Standard AR lower to accept MCX Upper
  • Back Up Iron Sights

This is a new OEM Sig Sauer MCX Conversion Kit that includes an MCX upper receiver, adapters to convert a standard Mil-Spec AR15 lower receiver to accept the MCX upper receiver, and a Sig Sauer two-stage trigger. The trigger installation is required to ensure proper operation of the MCX upper receiver. Using your existing trigger is not recommended and may lead to malfunction.

Sig's MCX conversion upper receivers include the necessary parts to install on an existing AR lower. That means you can essentially build your own pistol or SBR or convert an existing lower into a Rattler.

The kit includes the complete upper with 5.5" .300 Blackout barrel, bolt carrier group, buffer tube eliminator / 1913 back (for mounting a brace or stock), 1913 side folding adapter (for mounting a buffer tube for brace or stock), Sig's Match Duo 2 stage trigger, and a 1913 QD adapter. The upper ships with Sig's flip up sights too.

The Rattler has a two position gas valve for running suppressed and unsuppressed.

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