In the middle of an AR-15 build? Don't worry about all the parts at the butt-end of your AR-15. CMMG has you covered with the company's AR-15 Receiver Extension Kit, providing you with all the components you need to complete the receiver extension on your gun. Each CMMG Receiver Extension Kit includes the company's six-position receiver extension, ensuring that users get the most in adjustable length-of-pull from their guns. Combined with that are the Carbine-style buffer assembly and action spring, which are designed to run reliably with most standard, carbine-length AR-15s on the market.