A discussion on another board they were talking about this subject. (LR Forum). A Canadian guy I know lives up in Ontario which gets pretty darn cold, like -30 or -40. He said he's ran into problems with the small primers/flasholes in the .308 in the past during winter. To cure it they opened up the flasholes. Not sure which is the hottest SRP, I heard it was the Remington 7-1/2, but a thicker harder cup is preferred when running high pressures which is what this case is designed to do.
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ops...forgor to mention the smaller flash hole...if ya try these,make sure you purchase a thinner decap'n pin (.055-.057) or you'll get ur standard pin (.060) stuck...one of the few times that smaller is better....
Don't worry 6br.com updated their daily bulletin after you started this thread, I brought up the question about the flasholes in the comments on daily bulletin so they edited the post.
I've read that the small rifle magnum primers have the same amount of compound as the standard small rifle primer. So they are not hotter but the difference is actually a thicker cup. I use the CCI 450 Small Mag primer in 6BR-IMP cases because of the high pressures I'm running, the 450 is supposed to be one of the toughest along side the Wolf SR Magnum.
I do think this has some merit, but maybe not for hunting rifles. I will test them out myself when I get my Palma rifle built. Tierney won a 1000 yard Benchrest match in California with a .308 Palma rifle while testing this new Lapua brass. Once again humiliating benchrest shooters with his highpower prone equipment lol. Showing good chrono numbers and accuracy for American shooters, Lapua wouldn't have gone this far if there wasn't something to it, based on their own testing. That's pretty much a summary of what I've read on this stuff.