It was always thought that the small locomotives got new boilers when they were equipped with extended smoke boxes and shotgun stacks. This shot shows a shotgun stack with an original lap-seam boiler. It would appear the lap seam, which was across the vertical centerline of the boiler failed, launching the steam dome and peeling the boiler open. In the first pic you can see the failed lap seam. It looks like the riveted seam is still intact, while the boiler sheet split where the piece of boiler steel lapped over.