Given that reamers can, and usually do have an interchangable pilot, and modern barrels have pretty tight tolerances I don't see the problem....
Brent, I think part of the problem lies in the fact that the pretty tight tolerances of modern barrels are still open to interpretation and change by each barrel maker. For example the modern 40-cal barrels have groove diameters that range from a high of 0.410" (McMillan) to a low of 0.406" (Shilen) with GM & Douglas in the middle @ 0.408". Then there are the original 40-cals with grooves ranging down to 0.403" and the newest ones intended for the 405 WCF cartridge @ 0.411-0.412" or so. How about the 32-cal bbls with grooves ranging from 0.318" to 0.328"?
Just a few examples although perhaps the most egregious of them.
Regards, Joe
