The only time I have missed with a musket are when an animal is either next to water, on a raised or lowered bit of ground or next to a tree. For some reason, until they move, they sometimes seem to be in a spot where I am unable to hit them until they move somewhere else. It did this when I used a catapult as well before.
Also, as said by neiro, the bile damage I do with musket has increased since I did a large feast. So I would agree its bile dependant.