Hi 'Nando,
Taken into account what I wrote in my current thread on earliest handgonnes concerning often firing shot out of them, they might even be called the 'primeval blunderbusses'.
Apart from that, I like your piece of course. Do not worry too much about its being converted to percussion; it is known that only the really well firing specimen were converted in the 19th century.
Best,
Michl