Many shoot 75-85 grains of 3f in their 50 caliber guns with patched round ball for deer. Your gun will determine which load and patching/lube it likes best for accuracy. The slower twist guns (1:60-1:72") generally require more powder to get the best accuracy. The common 1:48" usually like 75-85 grains for deer hunting accuracy and power. I no longer shoot a 50 for my deer hunting. where i hunt the cover is very thick and even a mortally hit deer can go 100 yards or more which would involve crawling on my hands and knees for hours tracking a hit deer. I now use either a 54 or a 58 for my deer hunting cause I want to drop the deer in its tracks. I aim for the shoulders, and usually break both with my shot so the deer does not go anywhere. I lose some meat, but it is worth it now to have to blood trail a deer in the heavy laurel.
As for loading 50 grains or more in your trapper pistol, I would advise against it. I believe, 40 grains is the listed max for that gun.