Bruce,
I talked to more than one reborer when doing an article on the subject a couple years ago. The primary reason for not reboring to a only slightly larger caliber is not just reaming correctly, but because so many rebore jobs these days are requested for button-rifled and hammer-forger barrels. The rifling of both introduces differential stresses into the steel, which makes reaming AND cut-rifling to a slightly larger caliber very difficult to do consistently--which is why most will only rebore to a caliber somewhat larger than "barely" more than the original.
When Cliff LaBounty was still working, he developed a method of lapping the lands and cutting the original grooves a little deeper. But that meant the rifling twist would have to be the same as the original barrel. This meant a 1-16 twist .35 caliber barrel increased to 9.3mm would also have to use a 1-16 twist, not so good with 9.3.
If the article was published I’d be very curious to know where. I’d really like to give it a read.
