At the range yesterday I was experimenting with a load of 680 in my 7mmx41. The powder charge for each bullet was the same. I had fired about 60 rounds consisting or 154gr RNs, 160gr,psp Sierras, 175gr. psp, 150gr. psp bulk unknown manufacturer, 150gr Win psp. All had the same primers but the cases were not the same from bullet to bullet weight. for any one group the cases were the same. All primers were a little flattened but extraction was EZ.

The next and last group were 150 gr. REM. psp. these rounds had been in direct sun light for about an hour and were extremely hot to the touch. The first one blew a primer.I might mention that these are Winchester primers and I have been noticing that they do go in with less force than others have in the past.

I had a very similar experience happen to me last year. Hot rifle hot ammo, blown primer.FYI roger

Rog, i have some of the same experiences with a 243win. mauser action and when i got serious about it i found the headspace had grown a couple thousands.
just a thought, you may want to check it.
glad i thought to check mine.
Dave

a person should not leave any ammo in direct sunlight for that long , factory or reload if ever. as you have found pressures will get very high

this isn't at all uncommon. Heat and cold affect the powder. You will find that a load worked up at room temp. will be much hotter in the summer and less so in winter, I've noticed as much at 200 FPS difference between loads from summer to winter. One way to minimize it is the use of the new poweders which are designed to be much less temperature sensitive. (i.e. varget for instance) One way to minimize the difference is in you pocket. It's pretty stable temp there. While temp doesn't make as much difference in big bores, on small bore cases (like in varmit hunting) it can easily make the difference between a hit or a miss.