AR-15 Barrel Extension

AR-15 Barrel Extension

The barrel extension is the part the bolt actually locks into on an AR-15. It sits on the back of the barrel, and its ring of internal lugs takes the force of every shot. This United Defense extension is for builders and gunsmiths fitting a new barrel, or replacing an extension as part of a barrel assembly.

Features

• Internal Locking Lugs — A ring of lugs inside the bore lets the bolt's own lugs pass through the gaps, then rotate behind them to lock the action closed.
• AR-15 Pattern — Made for the AR-15 platform and its standard rotating bolt.
• Machined Lug Face — The rear face is cut clean and bare, while the lug openings have even, rounded profiles.
• Dark Protective Finish — The interior and outer surfaces carry a black finish, with the machined face left in bright metal.
• Headspace-Critical Part — The extension helps set headspace, the distance from the bolt face to where the cartridge stops in the chamber, so you need to check it after installation.
• Barrel Build Component — This part joins the barrel to the upper receiver and is used when assembling or rebuilding an AR-15 barrel.
• United Defense Manufacture — Made by United Defense, a commercial parts maker, and not military surplus.

Fit And Installation

Fitting a barrel extension takes the right tools and a careful headspace check with gauges before the rifle is fired. If you have not done this kind of work before, have a qualified gunsmith install it. Once it is fitted to the barrel, the extension slides into the upper receiver and the barrel nut holds it in place.