That's another good point Paul. I have used .30 /06 brass to make cases, and they work just fine. In fact, my RCBS dies came with a tapered expander plug for just that purpose, and it is even mentioned in the enclosed literature that came with them way back when I bought them. The plug is small enough at the bottom to enter a case as small as the .280 if I recall correctly, and has a longer than normal ball to allow easy necking up to .35 cal in one easy pass. All cases that I did that way came out straight and true in one pass, and I didn't have any troubles with split necks from doing it either.
I am betting that a 125 XTP wound up a bit in the Whelen would make for some impressive diplays out to a bit beyond 100 yards on shots on chucks.