Curious stone cannon

[Marcus den toom]

I don't really see the problem with the holes in this cannon.
The breechblock, which is sadly missing, would have had a touch hole. Whih also solves the problem of wear since you just could use a new breechblock.

>1 is behind the actually breech and could never act as a touch hole.
>2 looks to be drilled horizontally or at least at such a shallow slope that it would have emereged at the far end of china before reaching the bore (because once again, the breechblock is missing and can't possibly be connected by drilling a hole at least 20cm in front of the breech).
>3 is the mystery hole i was guessing at. If there is a hole there it would be likely a hole to move this cannon. We don't have measurements, but anyone with a bit of life experience knows that a piece of granit (one of the heaviest of stones) weighs a few "pounds". So logically there should be some way to move the cannon without having a 100 chinees man stampeding against one cannon while the enemy is raining arrows on them. There might have been a lot of chinees in that era as well, but i doubt that they where put to work in such a in effective way.
>Remains hole number 4 which again would come in handy to move a cannon (with a iron bar stuck into it? )

My question is how the breechblock would have been secured? In newer breechloading cannons the breechblock was secured by a bar which was put behind it or just by using wedges which would be pounded behind it.
Pounding near a stone cannon wouldn't be my idea of save working, seeing as a stone cannon is much like a handgrenate and even a small crack in this thing would have caused chinees new year to come earlier than normal (force always seeks the way of lowest resistance).