I did some calculations based on some rough measurements I took of that picture, and assuming that case takes a large pistol/rifle primer, then that cartridge has a rim diameter of about .566". The closest rim diameter in a handgun cartridge to that is the 500 S&W at .560". But, I could be wrong.
Formerly TN Lone Wolf
"We are only as strong as we are united, as weak as we are divided." - J.K. Rowling
Okay, so the rumors and the reverse engineered photo give us an idea of the possible calibers, but what kind of SA is it? BH, SBH, Bisley, Bisley Hunter? Is there any possibility it could be a 50 JRH? How about a 50 Ruger? ????????????????