Had no issues with expanding the .30-06 necks up to .25. Makes good Whelen brass. Go for it, just make sure you use a good lube.
Down through the years, making wildcat cases from .30-06 has been the way to go. While technically no longer a wildcat when I purchased my first .25-06 in the very early 1970’s, getting factory brass was all but impossible. So, got a .25-06 trim die (easier to get then the darned brass at that time) and made cases for years. Never had an issue. When we built my first .35 Whelen during the height (or depth) of the obama years, Whelen brass was unobtainium. Actually finding 06 brass of any size or caliber was difficult. Finally found a good sized batch of .30-06 brass and went to work. As I said, no issues, brass shot great.