stonehog Wrote:More photos. I was only able to find the slightest ridge forming on 2 cases. #9, and #36. #41 was the kaboom.
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These two pics explain/validate a lot. I keep studying them and seeing "stuff".
The line on the first two look to be at the same location, this supports the fact that the rounds were in battery. This also indicates the beginning of the feed cone.
This line is also clearly the weak point, as this is supported by the fact that the failed round is literally torn right there (or very close). The failure looks much like how when you fold a piece of paper to make a crease, then you can more easily tear the paper along that crease. And it is a known fact in metallurgy that when you permanently bend a metal, it becomes weakest right at the bend point. This clearly lines up with what Bill Alexander was saying about how feed cone depth is an issue with some barrels.
The base looks to be failed the most where the extractor was. This makes sense too because as the unsupported brass literally inflated like a balloon, it would have uneven pressure at the extractor as compared to the lugs. This is still speculative, but that's my premise and assumption unless more information is shed to light. Also, because the brass inflated (or flowed) more at the extractor, it also was under stress there, more than at the lugs. As such, that's where the blowout occurred! It initially blew out there, and then a tear line formed along the line, where the metal is the weakest.
Ok so with all this my failure model is becoming clearer and clearer. Great pics!