The 18.4mm mark on the breech end of the barrel,is the bore dimension when it was made in Belgium. If the bores are still original and not been honed out this makes it a 12ga. Any other guesses at this time would be just that, guesses. The Belgiums made quite a few guns and they are rather common. Many are well made, but just not marked as to what company actually made them. Many times they also will have a manufacture mark that would lead a buyer to believe it was made in England, but a little studying would show it was not. I have 2 Belgium made shotguns at this moment and they are good guns. Good going on the nice turkey. I am sure you enjoyed the hunt with a classic old gun.
