If I were hunting elk , and I only had one shot , I would call Hawk Bullets in Salem New Jersey. Talk to the owner , explain what you want to do and ask for a recommendation of the Bullets he makes.
I did just that for a Bear hunt in Newfoundland, shot a 500 lb bear , he ran about 45 yards and was DOA . I was using a Knight disc rifle at the time . Tried a few different bullets to get the right load.
Good luck,
Soup
