600X SEM of the barrel wall at the location of what appears to be the initiation site. The 150X showing the cleavage is on the first page.



The cavity/void is presumed to have been the location of a large inclusion that likely contributed to the initiation of the failure at that point - slag?
Dimples are ductal overload indicators
The "possible voids" are likely the manganese sulfide inclusions seen on the 200X above, and which would diminish the steel strength.

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