Hi Mike, how are you doing?
One thought that came to my mind is that Nando's cannon migh be part of one of those old
mittralleuse devices which used multiple barrels, the kind you have portrayed already sometime ago, in this very same forum...
I routinely shoot a 20" Brass
Verso, with a ~ 4 cm bore: it's heavy, and far from adequate as a hand weapon...
OTOH, perhaps the explosive power of XV C. BP gave much less of a kick, compared with that from XVIII C..?
Best-est regards y'all
M