Here's a slideshow with photos of a 3-pounder bronze militia cannon with lots of holes on top of the tube filled in with copper. I'm sure the holes to the right of the vent were for a Hidden-type percussion firing lock, but I have no idea what the many other holes were for, any ideas?

http://s17.photobucket.com/albums/b62/c ... 2326e8.pbw

For further info on this cannon, here's the complete posting I did on another board.

http://www.go2gbo.com/forums/index.php/ ... 135.0.html