The Sierra K Receiver Extension Kit is the proprietary mounting system for the Sierra K Buttstock. It consists of a reduced-length, mil-spec diameter, 7075 aluminum, 5-position receiver extension, a short heavy buffer (3.5 oz), extra power spring, castle nut, and quick disconnect end plate.

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*Item must be returned in unused condition and in the original manufacturer's packaging (if applicable). If an item arrives non-defective and accurate to its description, this guarantee does not apply and returns will not be organized in those situations. Please confirm compatibility and specifications with us regarding item B5 SRK-1660 SRK EXTENTION KIT BLK before purchasing if you are unsure.