I think that such a thing would shatter, burn and/ or melt upon firing - and all that would emerge from the muzzle would be fragments. Remember, even in a low- pressure cartridge (such as a shotgun shell), chamber pressure is well above 1000 atmospheres. In any high-pressure rifle round, chamber pressures often exceed 2000 atmospheres. Such an idea might be usable as pellets in a shotgun shell, but they would be irregularly- shaped pellets, so they wouldn't pattern well.