the military used pencil flare launchers many many years ago. they usually were for pilots in the survival kits. but that was ok until someone decided to take one of the launchers and the empties to load stuff into them. or adapt them to shoot .38 spl. shells etc. somewhere out there after the atf or uncle sam found out they made the manufacturers of them put serial numbers on them. to make them easier to trace and or register. penguin was a big maker of the flares and possibly the launchers too. i carried a penguin launcher with about 8 red and 2 white flares for it. when i bow hunt for emergency signalling.
flaming arrows don't go high enough or burn that long using lit toilet paper on them. and not only that i only carry 8 of them.
but no matter what do NOT make a pen gun. design one carefully if you must for the course. but do not make it.