Kind of thought it would be 6 pdr
tho, I don't know how much 6 pdr is in centimeters so that was it. :I
Widewing,
It's a british gun which always looks so simple..
They put a barrel and give it enough thickness and mount it with a hole big enough for the ammunition.
anyways, I don't remember that brits used 25mm, frenchies did for sure though.
for 40mm whole barrel looks too thick.