I recently picked up a 16# Big 50.
I already have a bit of experience under my belt shooting .45-70s and the .45-100.
I wasn't sure what the correct loadings would be for my rifle, but after contacting some other knowledgeable shooters who shoot these, most who'd experienced good results recommended loads of 1F Express in the range of 100-110 g compressed.
So far the bullets I've tried are just a 640g RN.
I've got a mould to cast 600g RNs also, but have yet to give these a try.
My rifle's in the typical "Buffalo Hunter's" configuration, a heavy 30" barrel, nothing fancy, just plain wood with Buckhorn Rear Sight. I've added the early pattern tang mounted Sharps "Sporting Peep" on it as well. It has the standard "Military" curved Buttplate.
Firing it is actually pleasant, no immense or objectionable recoil, about the same as my 12# #1 in .45-70.
Here's a picture of my galfriend, Miss Lil, getting ready to touch off another shot through this big cannon. Weighing ~125# she can easily shoot 20 rnd.s without even thinking twice about it.
http://img.photobucket.com/albums/v475/billc_sbio/Sharps501-11-081-1.jpg