Old gun----new problem....Solution on Page 3

[Drifter]

It is a complete upper from AA. I doubt it is a mismatch. I called them and described the problem but they never got back to me.
I will look into getting some headspace guages.

Not sure that it's reasonable to expect AA to fix the issue since you report that factory ammo works fine...

...Hornady 123 A-Max factory loads and it went without a hitch. This leads me to believe my reloads are somehow defective.

I still think you need to adjust your dies (and back off the charge weight a bit).