Want to PP for 45-70 BPCR

[Kurt]

Reaming the throat is not a cure all. In fact it might end up worse.
Don't think that 9# paper is thicker then 7-1/2# I have 7-1/2# paper that is .002" thick and I have 9# paper that is .0016 thick. The # is only how much the ream weighs.
Those Browning chambers will shoot a PP pretty well as they are. Just match a unpatched bullet diameter for the paper you have most of that is as close to bore diameter so you can still chamber the round with out having to use a cartridge seater.
Or adjust a undersized bullet with your alloy temper so it so it fills the grooves when the shot is fired.
This is just something you have to work out with your rifle. No one can give your an accuracy load for your rifle. They can just give you what works in their rifle and a place and where to start working up a load.

Kurt