One especially but not exclusively for engineers & tuners.
Can a barrel be bored out slightly in the case of an imperial .25 (.243) to the modern 6.35mm which to my uneducated mind, might not mean loosing the rifling.

Looking at fired pellets I never see rifling marks on the head but does any one with a BSA quarter bore see this with metric 6.35 pellets.

I guess taking a .22 barrel out to .25 would be a step too far.