This is a factory take off bbl. I'm thinking it was a die on some paper controlled machine. At a mid 1970s community college we had a paper tape drill press. Nice machine that did wonderful work for us students . Just fascinating to us.If the barrel was threaded between centers (likely), the thread was nearly complete when the operator screwed up and hit the end of the thread. The dog slipped on the barrel a little and, when he went to make another pass, he split the thread. The tool was dull, the speed was too slow, and cutting oil may not have been used. Not pretty but it probably worked fine for years. WH