The one thing that will surprise you is how dark black they are...I'd suggest you practice on an all black (no white, yellow or orange dots either) target at various distances from various angles. You might want to become proficient using cross sticks as going prone may not be an option depending on the conditions (high grass or deep snow). I wouldn't plan on being able to shoot off hand...depending upon how wild they are...you'll probably stalk and sneak up onto them from a knoll and shoot either prone or seated using cross sticks.
American Bison are one tough amigo...that is why the old Buffalo Runners used big cartridges in 44, 45, and 50 caliber...they shot clean through them letting air in and blood out...creating a pneumothorax...it sounds cruel but that is one of the sure fire ways to put one of these bad boys down.
A good friend tried a head shoot on a young bull with a .45 2 7/8" cartridge...(which by the way will take out any large animinal in North American and has successfully taken many in Africa) the 545 grain paper patch bullet went into the skull and slide up the side and lodged half way into the left horn. It knocked him out unconscience and they thought it was over....a minute or two later he got up, shook his head, and begain to slowly go about his business....then another round later in the brisket stopped him.
Better do your homework before you make any final decisions about cartridge and tactics.