Mike, the barrel is clearly stamped 9.3. It has been suggested by others as well that it might be a 9x72R. The gun was apparently made in Ferlach, Austria. It was proofed for nitro at the Ferlach proof house. The commercial 9.3x73R ammo would is unsafe to shoot as the projectiles are .360" or .366" diameter. The 9.3x73R A-zoom test round (snap cap) chambers and extracts easily and is purported to be the exact size of the actual round. Thanks for your help. Doug K