Here's a description of a Meti buffalo hunt from "Caesars of the Wilderness" by Peter C. Newman:
"The riders, their mouths filled with bullets, plunged into the melee of disoriented animals. Guiding their horses with their knees, the Metis kept their hands free to reach the loose gunpowder in the pockets of their buckskin jackets. After each shot, a palmful of powder was quickly poured down the barrel of the muzzle-loader and shaken home by hitting the butt against the saddle. Once he was riding alongside his chosen prey the hunter would spit a bullet into the muzzle, the saliva making it adhere to the powder during the split second needed to depress the barrel, aim it just below and behind the buffalo's shaggy left shoulder, and puncture the animal's heart. Experienced hunters reloaded and fired fast enough to down three animals in the space of an acre's gallop."
History books are often written from anecdotal accounts, so leave some room for the exaggeration of time.