Just pick a barrel that will keep whatever ammo you're using supersonic up to the range you're interested in. 5-600m is no problem even for a 16 incher. 1000 yard needs at least 19-20" depending on ammo.
really? I was under the impression the bullet got googly as it went transonic... how long past that point can you retain good accuracy?Actually, supersonic isn't much of a consideration.
Mickey - why don't you tell these guys what happens at Bisley. Beyond the ranges that bullets stay supersonic ;D