This, from another site I frequent, describing an 8 bore DR the fellow built. I'm posting it here so Nitro Express people can get an idea of what large diameter round balls can and will do.

"It is an 8 bore with Oregon Rifle Barrels"
"The barrels had rifling at 1@144, .006 deep. The breechplugs were machined and the hammers were extended to fit."
"The load was 300 grains of Fg, an 8 gauge Ox Yoke lubed cushion wad, a T/C Wonder Lube Cleaning Patch and an .820 cast ball. 1,425 fps. Loaned to to a customer for an African hunt, he shot a charging 525 pound male lion at 25 yards, flipped it up in the air and it did a one and a half summersault and landed on its back, facing away from them. The ball hit high chest, went the length of its body and exited through the hind quarters, shattering the pelvic girdle.
The power of these big bore guns is just totally amazing and until a person experiences it for themselves, they just do not understand."