To add: you can see a rust/pitted spot where the crack starts. The threads are rusty because although this was an unused bottle, it has been sitting around since before we built here, six years ago. I did some copper about that time over at mom's house, so probably bought it then. What looks like bubbled paint to the right, though, is condensation. The threaded part is bent some (to the left from this perspective), I think when it landed it hit torch-first, that gave it the leverage to bend and crack.