arquebus??
 

Today I picked this up at the auction where I won it. I thought I could judge it from a few photos. It was a lot with what the description also said were cannonballs and a miniature cannon.
When I went to pick it up this afternoon it turned out to be a really small thing. I had completely misjudged the size. The cannonballs also turned out to be a lot smaller, hence the misjudgment. All in all a disappointment, but hey, you can't always win.

I was under the impression it was an arquebus but because it is so small I have doubts about that. As you can see it comes out of the ground and there is a rusted or perhaps popped open hole at the bottom of the chamber.
It certainly has age but what exactly is it? Oh yes, the caliber is about 11mm.