bpBill,
I have a K31 that I reload for and load SGKs but at a much reduced overall length (i.e. 2.925") due to the short throat in my rifle, too. I don't want to hi-jack your thread because I also want the guys answer to your question about a substitute bullet close to the GP11 profile.
But I picked up something in quickdtoo (Tim's) link that I have been told otherwise!? That Hornady "New Dimension Die Set" set the shoulder back fully to the original cartridge spec (18 thousands! from 0.477" to 0.459"). I was told the Hornady ND dies resized to the chamber specs not the cartridge specs!?