Well MD is not to far off, I have taken one at 180 with a Hawken 54 caliber But it had a 35.5 inch barrel I was using 130 grains of 2F and a patch RB. This was one I built myself.
My rifle was made with the intention of using it at Friendship and had an extra notch in the open iron sight and had shot 17 inch sting measure groups at Friendship so I knew what it could do.
Beyond that distance a PRB not only drops very fast but has lost a lot of energy.
The main problem with setting up to shoot accurately at long distance with a lead bullet is the slow speed and rainbow trajectory so you need an exact distance and once you get very far out that means you must range find the animal with a laser range finder capable of the distance the wind can also play a big part in how far it is practical to shoot.
If you feel you must go with a big lead bullet a White rifle and a mid weight bullet say around 400grains is what I would suggest, also plan on many hours at the range and a sight that is capable of the range you wish to shoot, a heavy bullet will start slow and have a rainbow trajectory but will keep enough energy for a proper hit at long range.