Don’t own one but did put a couple rounds through a Shiloh Saturday.  I think there was a thread on the 50-140 a few months ago where they did some discussion on accuracy. My opinion is after shooting one….I don’t know how anyone could get a good group with that recoil.  But, then I am a recoil wimp!  Sure could ring steel with it though.
Bob

An aquatince of mine had one many moons ago. He didn't want to use black so he loaded smokeless ( don't know what) behind a 550 grain bullet and no filler.  Almost every other round  hang fired until one he counted to twenty without the boom so he thumbed back the hammer unlocking breach just as it decided to go off. It spit hot gas and brass shrapnel all over his arms,  chest, and face. Thankfully he had glasses on which saved his eyes.  Big cases with smokeless is not a good idea. There is a reason Shiloh advised against it. I saw it first hand and it wasn't pretty.
Flatlander

I had a C. Sharps in 50-140.   It shot it with 140gr of powder and a 698gr Creedmoor bullet.  It was way too much gun for me to shoot well.  As I've aged I learned a few things along the way, often the hard way 

Chris.

I bought my Sharps 50-140 new in 1984. I was still in my late 20’s living in Nevada. I used it for hunting big mule deer. I loaded it with an Elmer Keith load of 130gr. 3f, 10gr. Shotgun powder over the primer, 3/8” grease cookie over a card wad, and a 725gr. Home made paper patch bullet. The rifle was the sporting configuration. It was a great hunting rifle, never had to shoot it more than once at anything! I still have the rifle….
Side note: I shot at a big buck mulie one time in the mountains of Nev. he was standing on the back side of a big Ponderosa pine tree. I fired, the bullet passed clean through the tree and the deer and kept on going… rifle never was lacking in power!
Tom

...

Several years I assisted running target rig at the Vintage cups. Two rifle classes stalking and stopping. Stopping the biggest guns possible single shots and doubles. African rife calibers mostly some Buffalo guns too. 

They were only shot offhand crossing and charging targets crosser diagonal 25-50 yards depending were they took the target  The charger from 50 yards out to were shooter had to step aside or be hit by the charging target. Third target at 50 yards turned, from edgewise to full face to edge in a few seconds 

Watching many, my observation, some could shoot them very well for a while putting shots in a 12 inch circle . Some could go longer, others had the worst flinch you could imagine. We even had a guy let go of his rifle and it went flying after the first barrel fired. 

Groups ? Hitting a bucket offhand 25 yards is about as good as I would expect most people could do. There are exceptions Malcom McGregor could shoot big stoppers all day with no ill effects. He had one of the most desirable single shots I have ever seen. Holland and Holland falling block re stocked by Griffin & Howe to Elmer Keith’s specifications, Keith’s personal African gun.

Chris Christensen ASSRA Schuetzenmaster at Columbia was one of the better shooters with a 12 Gauge Rifled hammer double using BP and a single round ball. Less recoil than most, met the stopping rifle rule & very accurate. Chris won several events with it.

My favorite as a shooter would have been Chris’s rifled 12 but Elmers single shot would have been the bragging gun.


Boats

I have a C sharps that I bought in .50-140 it was very hard to get it shooting tried everything I could think of it came with. Two molds a Lyman  450 gr. And a RCBS 512 gr. I believe it shot ok with smokeless but not black . Finally I try some Buffalo arms 650 gr and some 700 gr. bullets and 130 gr. Of Goex ctg and my 200yard targets now had groups on them instead of patterns but I started getting a very bad pain in my right eye and said goodbye to the .50-140 now it’s a tack driving .40-65. Also I tried a lot of reduced Blackpowder charges with fillers that was a complete waste of time.