Aero Precision Epsilon 556 SL, Muzzle Brake, 223 Rem/556NATO, Black, 1/2X28 APVG100025A The EPSILON 556SL is the ideal muzzle brake for 14.5" rifle builds. Featuring an outside diameter of .745"" the EPSILON 556SL can be pinned and welded to your barrel while still allowing full maintenance and removal of your gas block without having to remove the muzzle device.