So if .428" tapering about .001" toward the muzzle, am I correct that 0.427 or smaller (0.426) is the appropriate bullet size? (that seems to match up with my physical comparison of bore slug to to the 0.427 resized bullets which seemed a hair bigger than the slug)

I can now see that the resized 0.423 bullets are too small. Once I run a crimping test on the 0.427 and 0.426 bullets. I will see if I still have a bullet tension issue or not.

Is wide neck clearance a normal situation or something to be concerned about? I ask this because I wonder if a previous could have caused it by firing cases less than half filled with powder (similar to chamber ringing). I have carefully reexamined for chamber ringing and I see no sign per pictures I have seen in books.

What size cast bullets should be used in this bore?

How will the B.BLINDEE rifling handle cast bullets?