I know the 450-400 3” has an improved, thicker rim than the 450-400 3.25” cartridge. Do they use different shellholders as a consequence of the rim thickness difference? What about 450NE?
450-400 3" uses its own shell holder
450-400 3 1/4 and 450 ne and bpe use the same shell holder.
I have both sizes in OD. I don't think any maker made one size but made them with what was on hand at the time or what the machines were set up to make. I had a local machinest years ago make some shell holders not made by others or I didn't want to wait months or a year or more.
Cal