That was a bit of a bummer, but to be honest, I was worried about those barrels as soon as I saw them. They stick up at an angle and were never going to be very strong. Transporting the Metzgers was going to be a big hassle.

So first thing I did to "fix" the model was to file down the area where the barrel broke off. After doing that I drilled into the cannon where the barrels were:

I used a drill bit that is a tiny bit bigger than a paper clip (if your pin vice doesn't come with one the right size, just take a paper clip to the hardware store and get a drill bit just a tiny bit bigger than the paper clip).

After drilling out the holes, I grabbed a paper clip and something to snip it with. I then snipped off the desired length of paper clip and then flipped the paper clip around.

It is important to do this as when you snip the end of the paper clip off, it will cause the clip to pinch into a point and I want the flat end of the paper clip showing.

So after snipping both ends off the paper clip, it is a simple matter of flipping them around so that the flat end is facing out and then super gluing the new barrels in place.

These end up being much stronger than the original barrels and whilst they are a mil or so thinner, they still look fine and I will pretty much just paint them as it.

If you were really keen, you could try drilling out the broken off barrel and gluing it around the paper clip or use some green stuff (or equivalent) to thicken the barrels.