SIG SAUER MCX AR-15 5.56x45mm NATO Caliber Exchange Kit 9in Black. Convert any M4/AR15 platform into a modernized folding firearm with superior reliability durability and accuracy. IMPORTANT: This item includes the Barrel and Gas Block assembly only. It does NOT include the Bolt Op-Rod or Handguard typically found in full Caliber Exchange Kits. Specifications for SIG SAUER MCX AR-15 5.56x45mm NATO Caliber Exchange Kit: Manufacturer: SIG SAUER Color: Black Caliber: 5.56x45mm NATO Magazine Capacity: 0 Round Magazine Included: No Condition: New Package Contents: SIG SAUER MCX AR-15 5.56x45mm NATO Caliber Exchange Kit SIG SAUER Infinite Guarantee SIG SAUER WCALX-MCX-556N-9B-LT: MCX AR-15 5.56x45mm NATO Caliber Exchange Kit 9in Black