The geometry of the muzzles of original rifles has been discussed many times. Various explanations have been offered for what I have often seen when restoring original rifling by freshing with cutters:
The diameter at the muzzle is 0.015” greater, more or less, than 5/8 of an inch to and inch and a quarter down the bore.
The rifling grooves at the muzzle are at least as deep as the grooves in the remainder of the barrel.
If you think about it, this cannot arise from either wear or deliberate coming as it is done nowadays, which makes the grooves at the muzzle almost disappear or disappear entirely.
Original poster: does this “rifling form at the muzzle of original rifles” discussion merit a separate topic?
Fine either way.