Agree. This falls into the “could have happened” category, like using gourds or canteens or wine bottles as powder horns in the Illinois region pre-1750.If we can document Bison/buffalo in the 1600's as far east as Florida, Alabama, Tennessee, Kentucky, Illinois etc. etc.
1700's inhabitants were using the hides for robes, bull boats, meat for sustenance and the wool for weaving etc. explain why they would not use a bison horn for powder just as soon as they would a cow.
I repeat there are zero documented bison powder horns pre 1770. There are hundreds of documented cattle powder horns pre-1770. If the goal is to settle on whatever seems possible and feels cool, without any likelihood attached, that has nothing to do with the original question, which was aimed toward what would be a likely powder container for someone in the vicinity of Fort de Chartes pre-1750.