How is the chamber lead angle determined?

[Kurt]

Todd.

I use a .44-70 Maynard sizing die for the .44-100 made by CH-4D. I still think you should shoot that rifle as it is. The free bore is not a problem for the PP bullet. It's just a matter to get the brass the proper length. What I think will give you a problem is the large head dimensions and the .475 case mouth with a .338 bore diameter. This will give you a .007" slop holding a .446 GG bullet and if you size the case down to hold a bore diameter .338 PP bullet that case will look like a bottle necked case. All the way around I see a problem. Even the Base diameter at .510 might give you a problem bulging a .503 base diameter case your brass is.
Having a 2.6 reamer made from that cast is not going to do anything but clean up the sharp chamber end and free bore you will still have that excess case mouth diameter.
Check out what I said for the dimensions and see what you come up with. I might be missing something here. I hope the instrument you took the measurements with is out of calibration.
I really think re chambering it to a .44-2-5/8 (.44-90 bn) is a better option if your measurements are correct from the chamber cast. But you will still have a large case mouth

Kurt