If you are still not getting the accuracy out of the REAL with the Plumber's lead try using less powder. The REAL's bands are quite thin and may be shearing in the rifling due to the velocity.
I am not too surprised about the lack of evidence for expansion on last year's elk, not because of lead hardness but because of the nose profile of the boolit. The first deer I punched was with a T/C Maxi Ball at about the same yardage as your elk. She tore out off into the foliage but I hear her slide through the leaves in a few seconds. She was dead but the wound showed no expansion at all, .50 in and .50 out. When I purchased a mold it was for the Maxi Hunter, which has a rounded nose profile. Those did expand some, as I have a few recovered in my collection. Still, a 50 caliber hole is hard to argue with.