CMMG Inc Receiver Extension and Stock Kit A1 MK3. 308 WIN platform firearm to a proper MK3 platform firearm. The receiver extension features two QD flush cups on either side for mounting the included A3 pistol grip and AR-15 style buttstock. The buttstock is constructed of an injected-molded high-strength polymer for durability and features a full-length adjustable cheek-piece and polymer extension stubby tube for customizing the look of your MK3 even more. This receiver extension and stock kit will work on any 308 WIN platform firearm but may require slight fitment fitting/fit behind a .308 WIN barrel. NOTE: Magazine extensions will NOT fit .308 WIN barrels. Check manufacturer recommendations to ensure a proper fit. Specifications for CMMG MK3 Receiver Extension and Stock Kit: Manufacturer: CMMG Color: Black Buffer Tube Size: Mil-Spec Gun Model: CMMG Mk3 Length: 15 in Condition: New Condition Quality: Excellent Condition Details: Other Gun Make: CMMG Weight: 2 lb Fabric/Material: Aluminum Polymer Package Contents: CMMG MK3 Receiver Extension and Stock Kit 6-position M4 Buttstock CMMG 6-position mil-spec Receiver Extension (Buffer Tube) Buffer Tube Castle Nut Receiver Endplate .308 Carbine Buffer .308 Carbine Action Spring What firearm models does the manufacturer say CMMG MK3 Receiver Extension and Stock Kit is compatible with? The manufacturer says that CMMG MK3 Receiver Extension and Stock Kit is compatible with CMMG Mk3CMMG Inc 38CA964: Receiver Extension and Stock Kit A1 Mk3