.400 Whelen is out, just too wildcat for this dumb country boy.
Cash,
For what it's worth, the 400 Whelen is a pretty simple wildcat to feed. Reasonably priced dies are available from CH4D and cases are easy to make. I love mine. That being said I'd want a bit heavier barrel than the standard 30-06 barrel on a 721 for a 400 Whelen. Recoil might be a bit noticeable if one rebored the standard barrel to 400 Whelen.
Don't pay any attention to the trolling 721 detractor. You've got a good rifle and it is well suited to reboring to 9.3x62. If you go with JES, you'll only be into the rebore around $250 with shipping. That makes a pretty reasonable way to get into the rifle. Anything available on the market in 9.3x62 is going to set you back way more than a rebore from JES.
I've had several 721 over the years before I started changing over to left handed. Never been disappointed with a 721.
