Been times on the trail, not often, but times, when going to prime for my turn and the pan is full of wet black goop.
This is wiped out with the shirt tail of someone who isn't watching, or a piece of flannelette carried for the purpose. Then prime, step up to the line and fire - no problem.
I suspect the problems arise when hunting small game like squirrels, bunnies or grouse, where multiple shots are fired and one must wipe and re-prime often.