If it doesn't seal up tight when closed you'll more than likely leave a trail of 4f on the ground...take the lock out of the stock and with thefrizzen closed look for any daylight along the seam. Some folks like to seal the edge with grease, just make sure it's cleaned off every shot and that may keep things sealed up enough

On the slow burn thing... it may be only noticed if the gun doesn't go off.
Sounds like too much powder, keep it downto 1/3to 1/2 full and make sure you pick the holeevery time you load. If it doesn't go off pick it again. May need to open it up slightly to 1/16"