A-C-E has reviewed the .950 JDJ round (shown in the bottom right image on this SSK page) in an earlier post.
The McBros .95 caliber rifle appears to be the rifle which could fire it. It was probably a special project for JD Jones. (Neither the round nor the rifle were ever produced in any appreicable volume). It weighs 86 lbs.
In comments to an earlier A-C-E post, firearms historian Daniel E. Watters had this to say about the .950 JDJ (a project round by JD Jones @ SSK Industries):
"The custom single-shot rifles for the .950 JDJ reportedly weighed over 100 pounds, I really doubt that you could make a manageable handgun out of it. (The muzzle brake alone weighed something like 18 lbs.)
Remember the ballistics, 3,600 grs at ~2,200 fps."
That works out to 38685 ft-lbs of energy at the muzzle.
McBros was founded in early 1992 by Rock and Kelly McMillan.
This, and the .50 BMG, come closest to the ability to knock a man backwards (if the round hits a major bone structure like a hip), as is so often depicted in Hollywood (even with pistol rounds).