FWIW, I have one of those Carcanos converted to 7.9. I fired it a couple of times with German sS ball with no problem, but I did so carefully as the larger cartridge not only has a greater working pressure than the original rounds, but the larger physical size of the 7.9 round reduces the amount of metal in the barrel and receiver.
I would have to say the gun didn't blow up or do anything else wrong, but I do NOT recommend firing them. The Carcano, in its original calibers, is actually not a bad gun.
I once said that if I had been a soldier in 1891, I would have preferred a Carcano to the rifle the U.S. Army was using at the time, the trapdoor Springfield.