I'd hope for better than six inches at a hundred metres if having the barrels reregulated. Assuming the 150 m at 100 m was that.

For a .45/70 I guess its usable though, as its not a long range rifle.

How does each barrel group? If they group far better, the angling of the barrels to make them coincide should be done.

Hope it works out for you.

PS yes get copies of pictures of the "groups" before they finish everything up.

PPS Im thinking the 6 inches is a completely off hand shooting group at 100 metres. The free hand, unsupported etc comments. I think a supported hand on a rest would be used for testing shooting a regulating rifle.