The striker indents appear to be wanting to reverse flow. Normally the M16 requires a very hard striker indent to reliable ignition which comes with deeper fired primer indents. If the hammer spring is not up to spec the pressure rises, allowing the striker to head in the other direction. I had this bad on my 7615 and checked the striker energy and it was too low. I replaced the hammer spring with new Wolf spring and the indents now look correct.
This is normally tested by measuring the depth on a pressure copper in a copper holder that looks similar to a headspace gage. The SAAMI standard for 223 now is .016" indent depth and was .020". The M16 spec calls for .022" indent. The hardest primer to ignite in US inventory is Cal 50 followed by primers for 5.56MM.
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