Hi CJR, I was surprised at how bad it shot too. But I am right with you on the theories.
#1 - Yep, seated to it engages the rifling a bit. Not huge though since there is barely any bullet in the case now.
#2 - They were .309", I wish I had some slightly thicker paper for .310.
#3 - I totally agree. I suspect the filers I got were from voids inside. Hitting them this hard is going to likely reveal flaws that normal cast bullet loads don't show.
#4 - Yep, I learned that. I had some primed with Fed 215s and some with Wolf LR. The Fed ones hit higher and were more accurate. The Wolf primed ones had quite perceptable hangfires and hit lower.
#5 - I think this is a problem with these boolits. They weren't very hard, and do have a fairly long unsupported nose and a very large meplat. Next time out I'm going to shoot #311466 Loverin style boolits, from my new NOE mould. A short round nose and almost all body should take the launch better. I expect I'll see better results from them if the theory is correct. Those NRA paper patch bullets look like that as well, so that's some sort of verification.
#6 - You're right about the vertical. I had lots of wind so I would expect to see lots of horizontal, but the vertical is powder charge and primer. Going to only hot primers should stop the inconsistant ignition, and once I get a boolit that shoots predictably I can start doing ladder tests to home in on the ideal powder charge. I also want to try some WW780 to see how that works, since it'll allow a full case instead of some room like 760. I suspect it'll work even better but don't have any yet.