Handgonnes with iron stock

[Matchlock]

Hi 'Nando,

That's what I would like to now too but the museum catalog I scanned the image from does not provide any measurements, and when I attended the Musée de l'Armée by special appointment and was allowed to photograph anything I wished to, the Medieval Department was sadly closed.
Thus I could not see or access the piece but I estimate its overall length to be ca. 60-70 cm, which would make a bore of ca. 20-30 mm seem reasonable.
As the barrel walls seem relatively thin it is probable that, as was often the case, the originally smaller 'bore' was widened during the later working life of the gonne.

Best,
Michl