Crush Washers and Shims for AR Rifles

To properly mount most muzzle devices on your AR, typically you want to use a crush washer. This part “crushes” against the shoulder of a threaded barrel, providing the necessary tension for your muzzle device to stay aligned properly. For muzzle brakes, flash hiders, and compensators, a crush washer is typically all you need to use, and it’s easy to do with an armorer’s wrench.

Shims, on the other hand, are most commonly used for suppressors, and suppressor mount muzzle devices. Shims help to ensure these devices are concentric to your rifle’s bore, and you may need multiple shims to achieve correct alignment. Always use shims if a suppressor is involved; if you don’t, you increase your chances of a baffle strike, or other failure.