Krautgunner beat me to it. Blackpowder. Just a wad andnot lead ball. Safe, noisy and a loud boom! Plenty of muzzle flash, plenty of smoke, lots of fun.
BTW, I want to go to a Russian funeral now that spacemanspiff told us about the 10 minute 300 gun salute. I'd like to be #301. I'm presuming this is all birdshot so it won't go far.