From time to time, if you don't block the vent prior to loading (and I never do), a piece of fouling is pushed into the hole with the force of loading, and you get a misfire. It happens but it's rare, and I do like to see the charge right out to the pan after loading. In the event of a flash in the pan, one needs to clear the vent of fouling, to allow the pan flash to enter the vent.