Bigger and cheaper
If you want something to make your friends jump out of their skin and doesnt cost alot, buy an old Thompson Contender in a 12 inch barrel chambered in 45/70. Its a handful and its great for clearing the gun range when there are idiots around LOL. I once fired one in an inside range and since my barrel wasnt clearing the partition, if was deafening.
Ballistically Speaking, Im about a 300 FP with a BC of -1.