This was taken from a two low resolution pictures that were available to me from the previous owner. Lines are drawn at equal length, top and bottom of the cylinder. Image enlarged to 300% for easier viewing. Despite the low resolution, I am fairly confident that the frame was not stretched when these photos were taken. I consider the "who dun it" to be solved.
edit:
Going through my camera and finding other pictures, putting together the history, this damage would have occurred within the first 6 to 11 shots, as that is all I got through in my first day of shooting. Those shots would have been about .371 diameter, and the barrel was unlubed. (Bullets were lubed, barrel was not)
In the ~40 shots since then, the crack has not changed.
More gun #### - 6 shots in:
edit:
Imgur seems to reprocess my image. Zoom+darken+sharpen =
Same size and shape of crack as currently exists after ~40 extra shots.
ehhhhhhhhhhh..............
I'm likely going to kill this gun now, unintentionally, in the name of pseudo-science. Since this thread practically insists on it, I can wear a steel helmet in addition to my ballistic goggles and deerskin gloves. I've got a steel mesh that I can use over my face, too, just to completely eliminate the possibility of serious injury. There's no point in shooting it out of a vice. If it dies and I still get seriously injured, as statistically unlikely as that is, considering the crack location and safety precautions, I probably deserve it. The only way I could possibly lose digits, wearing deer skin gloves, is if I was holding it wrong, if all cylinders exploded at once, or if the receiver broke off at the rear on the bottom, which it clearly would not.
I'll try slugging the barrel with one of the new bullets, to compare difficulties, before shooting it, of course... that said.... I'm going to shoot it. For pseudo-science.