I believe this is the first time in my 73 yrs that I've ever read or heard of anyone ever using black powder in a 9.3X74R cartridge! Since it was never loaded with black powder but was a smokeless cartridge from its inception. In a double rifle I doubt it would develope enough speed, or recoil to shoot to the regulation of the rifle, since all double rifles were regulated with smokeless powder to around 2360 fps with a 286 gr bullet! This is just a thought but the 9.3X74R cartridge is NOT a black powder cartridge!
Do you have any idea what every posessed him to use black powder, and what kind of results did he get?