I agree that fast powders are NOT what the 10mm was designed for, but they are perfectly safe and this in no way looks like a double charge.
That is NOT from a magnum primer. That is NOT from a slightly low COL (and, no matter what the COL is, you still start at the start load).
Reloading mistakes generally show up around the extractor groove: Guppy belly, blown out at the web, blown out through extractor groove, or bulged case head.
All I could say is that based only on my experiences, that is a case that had an inclusion that weakened the brass at that point.
Here is a picture of an overcharge:
That is NOT from a magnum primer. That is NOT from a slightly low COL (and, no matter what the COL is, you still start at the start load).
Reloading mistakes generally show up around the extractor groove: Guppy belly, blown out at the web, blown out through extractor groove, or bulged case head.
All I could say is that based only on my experiences, that is a case that had an inclusion that weakened the brass at that point.
Here is a picture of an overcharge: