After getting the barrel of and doing some measuring I found the barrel was swelled in the tenon, I bore scoped it and it looked to be fairly carboned up early in the bore so I ran some bore cleaner just to brighten up the copper fouling. The fowling was heavy, and had a peeling look at the edge of the rifling, I used a reamer bushing and sized it to be just snug then I cleaned the snot out of it, it took some aggressive cleaning but not like it was the worst I've seen. There was a fairly continuous coating of copper from about 8 inches in all the way to the muzzle which is a fair bit. After cleaning the bushing did fit much easier but I couldn't get another .0004 larger bushing in.
I did try to measure bore movement based on temp and through a -20 to 40 degree temp swing I could measure no change with a bushing inside or a precision Brown and Sharp digital mic which can easily read tenths so I don't think temp constricted the barrel.
It was more than poor brass since there is massive evidence of way more pressure than just a poor case and I don't think any other brass would have changed the outcome. and no evidence of a length issue.
The OP reloading practice looks solid, no way to double charge, really no way to even over load to this level. Jambing a bullet will not take you from OK to catastrophic.
I don't think the fouling helped the situation but I'm not convinced it was a cause unto itself.
Detonation or bridging, something to do with how the powder lite I would say could not be ruled out or explained.
In the end I think all a guy can do is make sure follow some of the basics of reloading, one powder out on the table, keep brass in spec, when changing a major component clean the barrel cause done right your only helping yourself and your equipment, these are things within our scope of total control, beyond that I think some odd things happen every once in a great while that can not be explained and may never and that is why we do our best with what is totally under our control. I honestly can't see anything I would do different except clean the bore between components but unless the bullet would be welded in the bore the physical evidence is so minute it would only be an guess the exact chain of events if there was one.
