Gamebore in the U.K. are the only manufacturer of Black Powder cartridges as far as I know. They only do them in 12 and 20 bore but did a few in 16 bore once. Quite expensive so far earlier to make your own. One thing to watch for with today's so called light one ounce loads is that a lot are made to function through semi autos so have a bit of pressure. If you live in Ireland I thought there was still a Proof House in Dublin that you could consult with. Lagopus.....