I agree with Mark
You can do the math on the tapers of both cases, and I think you would have to set it back at least 3/8 inch to not have some sort of step, or void, where the originol 30BR chamber ended.
I have set back a lot of chambers. Unless you know exactly how the Gunsmith set it up originolly, it is sometimes difficult to even get the thing running true.
That being said, remember, the reamer is going to try to follow what ever hole is there anyway. Try as you may, that is just how reamers work. The only way you can affectivly change that senario is to single point cut what is left, and as you will learn, that is not easy to do with such a small amount of material to play with.
In the end, it might not be a big deal to have a little step, or void, in the chamber anyway, especially if you full length size. It will be up toward the shoulder, as opposed to being near the web, where it would probably be more of a detrement.
Some of the Ackley chambers I have seen, (usually when attempted with a existing Factory Chamber), have distinct steps, and wallowed spots, and other things that make the purist roll his eyes
........jackie
