Originally Posted by Big Cholla

Good pictures and I don't see a 'crack'. I see a flame cut. There is additional proof just to the left of the flame cut where the lip of the barrel forcing cone shows another form of flame cutting. I think that your barrel/cylinder gap is/was bordering on 'too much'. In any batch of metal parts of any firearm, there will be one or some that have an anomaly in the grain structure of the metal's meld someplace. IMHO, That barrel happen to have one right at the location of the exhibited flame cut.