I have a tompion for my fowler. They are fairly easy to make. You will need an over bore size dowel, which you then trim down to bore size. The portion sticking out of the barrel( the head) can be made into any shape you desire. That is how soldiers distinguished their guns by FEEL in the dark. You do need to think about making two cuts at right angles through the length of the tompion, so that the 4 arms are able to expand and be compressed when they are inserted in the barrel. My Tompion is about 6 inches long, and 5 inches of that goes inside the barrel. I just soaked my tompion in oil for a couple of days to help swell the arms. I probably will need to soak them longer, but this may work. Some people use felt, or leather to make a washer for the underside of the head, and glue it to the bottom of the head to act as a seal to the muzzle if the gun is to be left outside during rains. Either felt or leather can be soaked in oil to help seal the bore.
I don't think you are going to have any problem about losing the Tompion. Tompions are put in empty guns, not loaded ones. You have to remove the Tompion to load the gun. Since it cannot fit as tightly ( at least in a smoothbore) as a real plug, it is not a substitute for tape, or some kind of leather or waxed paper cover for the barrel during rain, when the gun is loaded.
Some people make a special loop inside their range bag for the tompion to be stored when not being used. That way its not misplaced, or lost. There are fancy models of tompions, and the sky's the limit on how they can be carved or decorated. Some have antler heads, others made of horn, other of some hard wood that takes carving and inletting well, so that wire inlays, or metal inlays can be added. I have seen one tompion that had a beautifully carved wolf's head on top of it, with inlayed jewels for eyes.
I am thinking of cutting a groove in my arms, to allow the use of an O-ring, which will both seal the bore, and keep the tompion from moving and falling out of the barrel. If not an O-ring, then some waxed string thick enough to provide greater friction with the bore. I have a lot of synthetic sinew that is waxed that I can try to use. If it works, I will report back on it.
