The Carcano got a bad rep because a large stash of Italian mil spec ammo sold in the fifties and sixties had been found stored in a cave in Egypt. That ammo was loaded with an early double base powder with 60% nitro and had degraded past safe use. Firing a few of those was equivalent to the C4 charge used by one test to blow up a Carcano. C4 has a 58 Percent nitro content same as Bullseye and Mk1 Cordite.
When older double base powders or cordite are subjected to temperatures of 125 degrees or more for any length of time the nitro sweats out and settles inside the case.