Chuck;
You can quite easily calculate how much wt reduction you will get for a given amount of metal removed, I know you are aware of this. As to pattern enhancment I would be skeptical. When one considers all available types & sizes of shot, all usable powder types & charges, all hulls & primers availabe you would likely end up with some 37 million possible combinations to be evaluated. When someone says the backbored a bbl & got immediate dramatic "Improvement" well did they change the degree of choke? did in the process they change the angle of choke etc, etc. There is so much to be considered I would simply not look for any magic to happen because of a few thousandths difference in bore size of a nominal gauge.
I have shot different guns of several gauges with bores standard, oversize & undersize. I have not done enough extensive pattern testing to really speak athoritivly, but from a practical use aspect I really could never tell if a bbl was +.010 or -.010 in either shootability or recoil, in spite of the many claims made to the contrare.
I think it highly likely that many making the claims have likewise not made extensive enough teating to speak athoratitivly either.
Perhaps a given bore size would enhance the "Fit" of a given shot size in the bore, but could just as easily give a less good fit of a size just one number off. Possibilities are endless.
