Do a search for Michael Petrov’s articles on the 400 Whelen. He does a good job of dispelling the headspace myth. In short there is no headspace issue.
It depends on the gun. You may need to do do some work on the rails for feeding. My model 70 feeds fine without any work. Except for the short Hornady flat points and the 300 grain Hawks.
Chronographs, bore scopes and pattern boards have broke a lot of hearts.
