If I'd had time I'd have pulled all the pistons out, but I was pressed so just boxed it up and shipped back to Mopar for core once we found the one disintegrated. I received some piston/rod assemblies from a performance shop (3 assemblies) from a failed engine. They didn't give me details on what failed, but
@16GoManGoHC2 has experience testing parts failures so I shipped two of them to him to do some catastrophic tests on out of curiosity. I also sent him what was left of my #7 cylinder piston. Piston tops looked ok on the three test subjects, but had some scoring on the sides.
Turned out the piston assemblies I sent him were bent (granted not from my motor but AJ has mentioned bent rods more than once now). I kept one for myself as a souvenir and when Mike told me the others were bent I checked the one I kept, sure enough it's bent. The piston from my engine exhibited very similar wear characteristics on opposing sides as the assemblies I provided with bent rods. Mike's experience suggests the rod failed and caused my piston to fail. All just educated theory though really.
Had another shop reach out to me last week. Three Hellcats and a Demon all broke #7 and his analysis showed rod issues so they now recommend a piston/rod upgrade after 800rwhp.