Popped primers? Ambient temperature?

[thefitter]

Friday I shot these loads:

8208 XBR - 155gr Scenars - Lapua brass - CCI BR2

44.0
44.5
45.0
45.5
46.0
46.5

Saw no real pressure signs. 46.0 seemed the most promising.

Today I shot this:

45.8
45.9
46.0
46.1
46.2
46.3

First group I had a little bit heavy bolt lift that seemed to go away as I progressed through the groups. Weird, right? Second round of the last group I popped a primer. First time that has ever happened so I thought it was maybe a fluke. Tried one more and popped it also so I did not fire the last 2 rounds in that group.

The only possible difference between today and Friday, is that maybe Friday was 5 degrees cooler. But that is a guess. No real glaring difference in temperature.

I can't believe that 5 degrees can do this. Especially with 8208 which is supposed to be temperature tolerant. What else could it be?

Thanks

 

[Romulus]

What is the situation of the brass? Sometimes necks that are too thick can cause problems all of a sudden, but that doesn't sound like your problem.

Do you oil your barrel between outings?

 

[thefitter]

What is the situation of the brass? Sometimes necks that are too thick can cause problems all of a sudden, but that doesn't sound like your problem.

Do you oil your barrel between outings?

Very light cleaning Friday night. Totally dry, no lubrication. Same way it was before the first outing.

Thanks

 

[Shynloco]

The fitter,
What is the caliber of your rifle, Trim Length of your brass and OAL on the Loaded Cartridge? With both the tight lift of the bolt PLUS the popped primers is an indication of pressure. Personally, I believe theres no way it was the ambient temps that caused your problems. I just loaded some very similar test rounds in .308 but using CCI BR4's with VVN150, same Lapua Scenars, but won't be able to get to the range until Thursday.