pic of a very similar hand cannon to my piece
as it has the yoke to rail mount the gun [looks like an oar lock ]
and the extra bit on the end to attach a bamboo part so you do not hold the hot gun
the bamboo also helps with recoil and aim
but these are close in shot guns
http://www.acant.org.au/Articles/MalayCannons_files/Lela_miniature.jpg
from this site pic is about mid page
Cannons of the Malay Archipelago