Kroil, KW knock it loose and maybe heat from propane torch when you know for sure it's unloaded. Once out, replace with a allen or hex head screw and use screw driver slot head screw for re enactment or rendezvous. Don't forget to add allen wrench to shooting bag or loading box. Rub with some anti seize compound for auto parts screws, spark plugs, manifold bolts, etc. for easy future removal. It doesn't hurt a thing to occasionally unscrew it and clean and lube that part of the breech, drum or snail. Just make sure to shoulder head of screw tight or flush with side of drum or snail when re installing. Excessive removal of drum will wear the thread and cause misalignment of hammer nose to the nipple or a loose drum with play. I don't recommend trying to shim it with washer. . A sufficient number of fine threads and length of clean out screw should not offer a safety concern. Some hunters will unscrew the nipple, add some 4F powder in the drum and re screw the nipple, This is added insurance that the firearm goes bang when you pull the trigger. The clean out screw can be unscrewed to run a vent pick in when adding powder to a misfire in the nipple doesn't work or fouling or wet powder needs to be cleaned out of breech face and unfired load needs some help from dry 4F added. . Haven't heard of any accidents where an adjacent shooter on the line has been hit with a blown clean out screw or vent liner (flint). But have of blown nipples on percussion guns.