Hi footballboy5571,
If you really like getting hit...I've taken a few pretty good shots upon landing during sky diving. Usually the landings are pretty soft....but once in awhile[:@]. I guess if you are just looking to take a "big hit", skydiving without the chute would be a gas[

]. (Don't think you get to do it twice though

.)
But if you are just looking for good old pain from the butt of a gun I'd think that if you took a .450 Marlin Guide Gun, take it to a gun smith and have the barrel shortened from 18 to 16.25" (remove the ports), have him remove the recoil pad and fit it with either a steel or brass cresent shaped butt plate.....you could probably experience all the recoil you'd like. And you could shoot it for considerably less money than any of the older express cartridges.
If you decide to "give it a go"...and after a couple of hundred rounds that proves too tame. Come back and we'll think something else up!
P.S. I hope you understand all the above is meant in good fun!