For 82 oz's, I would need a hand rest unless I was throwing the gun at the target. Even then I would probably declare a timeout so I could tape it to hand with duct tape and take some pain medication.
"God made the world, but it's held together with duct tape".
http://www.exploremaine.com/~joeho/tape.htm
The pain medication is only necessary if you insist on perpetually shooting the largest rounds. Holding 5 1/2 pounds with a nice arm's length isosceles grip requires staying is adequate shape. A nice firm grip is a good idea too, unless you favor a dented forehead.
The Magnum Research BFR 45-70 revolver is a special case. You really want to fire that one with one hand and let it roll upward. A two-handed grip can literally smack you on the forehead with that single action revolver. The barrel on my BFR is 10 inches. The cylinder is 2 inches to accomodate the 500 gr bullets.
