Your cases look like this
this is a varient btw
A .243 belted magnum
Who says bolts aren't strong
Thats what happens when you use 42gr of H4895 behind a 95gr SMK and shove it .020 into the lands. The 42gr was a mischarge and should have been 39gr.
Edited to explain how this happened.
To charge a 243 you have to use the small tube to feed the powder into the case.
When using slow burning powders sometimes the powder will hang in the charge tube dropping less in one case and more in the next. You always visually inspect the levels but when the charge is down below the shoulder it's hard to tell the difference in a few grains. Quickload figured this charge from the velocity reading to be around 78000psi.
17000 psi over the SAAMI spec.