My method of fitting a brake is to chuck the chamber end of a barrel in the lathe chuck and support the muzzle at the other end of the lathe by the tailstock with a live center in the muzzle.
Very accurate to get the threads perfectly concentric to the axis of the bore. BUT, it also basically ruins your crown by doing this.
No worries though, every rifle I brake gets about 50 thou cut off the muzzle end and recrowned anyway when the brake is fitted, just part of the brake job and a requirement because of how I support the barrel for machining.
I would suspect most of your accuracy increase came from three areas, better trigger, Much better crown and the fact you did not have to worry about recoil /ubbthreads/images/graemlins/grin.gif!!
I would agree, recrowning a factory rifle is very cheap and often provides good returns on your money!! The sad thing is that to cut a match grade crown, it takes about 15 minutes at the most and the proper tooling and piloted cutters. Its a shame the big rifle makers can not take 15 minutes to get it right.
Kirby Allen(50)