The conventional advice I have heard is to use a fouling shot before shooting for effect. This means firing a shot in the morning before putting in your hunting load and then needing to unload at night before cleaning. Repeat for each, or at least every other, day of the hunt. I can not believe the fur trapping participants, or other early settlers and frontiers folk for that matter, did any such thing. If nothing else they did not have powder and lead to waste. Rather I would guess, particularly for the fur trappers, other than maybe a conflict situation, firing a shot was very infrequent. But I would also guess they would want to carry a loaded gun, and that a given load might be in the gun days or even weeks, maybe even longer, before being fired. Assuming my speculation here is correct, they would want to give their gun a pretty complete cleaning after each shot before reloading. Accordingly their hunting shots would almost all be through a clean barrel? And would not perfecting clean barrel accuracy have been important?