[ZeroJunk]

I have spent thousands of dollars on turkey shoot barrels,some backbored,some backbored and sleeved .They are for small shot,but may be instructive.

You can build two as identical as possible and often one will shoot better than the other.

If one shoots 9 shot exceptionally well, it may not shoot 10 shot well at all.

When you back bore you are in effect increasing the amount of choke.This does not guarantee a tighter pattern with all sizes of shot.

You can either decide what you want to shoot and find a barrel that likes it,or you can find a barrel and see what it likes to shoot.I would expect a modified or full choke to tighten up your pattern,but that may not fit with your other loads.