I have run into this several times in the past...
The Redding bushings have an angle cut at the mouth to help feed a larger mouth from a fired case, into the smaller bore of the bushing. The feeding bevel has sharp corners, and they leave scratches, and/or a sharp ledge in the neck that does not iron out with the loaded bullet.
And, of course, because brass can scrape off at the sharp edge of the bevels, it can lead to neck scratches...
That sucked!!!!!
So I got a 20° plumb bob, and chucked it in a 1/4" hand drill.
I wrapped the nose with #2000 grit carborundum "Wet n Dry" paper, and oiled it.
This is what they looked like after they were polished...
And this is what the necks looked like when loaded - compare to the loaded neck above.
I will tell you this - you will NEVER enlarge the bore of these bushings, no matter what you do.... They are God awful hard.