You are probably on your own on this one, but it will work just fine IMHO. Forget all the baloney about not enough shoulder and just go do it. I'll bet that you will be very surprised at how well it will work.
Get Vol I of PO Ackley's manual and read it through at least twice before you start loading. On page 483 he calls it the .375 Whelen and .375 Whelen Improved. Loads are for 235 gr and 350 gr. that will give you a place to start. RE 15 was not available in their day, but I would call Alliant and ask them for a starting place.
Maybe Ken Howell will post here. I think that he had a gun like that that he used with lead bullets.
