Without filing paperwork with the ATF, AR-15 barrels must measure at least 16 inches long, and once you add in a muzzle device, you've got a rifle barrel that might not be as nimble as you want it. Pinning a muzzle brake to a short, 14.5-inch barrel can bring the overall length up past 16 inches, but once that brake is pinned, there's no going back. However, the Aero Precision Epsilon 556 SL Muzzle Brake makes that permanence a bit easier to live with. Each Aero Precision Epsilon 556 SL Muzzle Brake measures 0.745 inch in diameter, which matches the profile of many popular AR-15 barrels on the market. This means that there's a seamless transition between the brake and the barrel, allowing users to slide a gas block over a pinned-and-welded brake without issue. You can't do that with your A2 flash hider! The Epsilon 556 SL Muzzle Brake, though small, still has a definite impact, as its chamber design redirects muzzle gases to significantly reduce recoil. The channel cuts on the brake also reduce weight at the muzzle end of a rifle, making for a handier carbine design.