I have a new Weatherby Accubrake for a number 2 coutour barrel and am wanting to install it on a Vanguard re-chambered from .338 Win Mag to .340 Weatherby. I have figured the thread to b 9/16" - 24 t.p.i, what puzzles me however is the exit hole through the centre. I measure the hole as it comes new at .395", that is a good .055" above bullet diameter . Is there an optimum clearance size for a muzzle brake any given calibre and in particular for a.338 bore? I make the assumption that the lesser the clearance the more effective the brake will be, from my reading of Weatherby's web site it may be that they used one size of brake to fit the .340 - .378 bore rifles as they appear to only offer 4 sizes of brake for the entire Wby calibre range. Whilst I have no doubt the brake will work to some degree am I wasting my time screw cutting the barrel to fit this particular brake to a .338" many thanks Jonathan BTW I am not totally new to LRH, my old password and user account/e-mail address were on my office computer which I no longer have access to so am now resorting to my home PC as it proved quicker to re-register a new.