I've hunted in below zero F temps quite a bit, all over Alaska... I never changed primers in any cartridge i've ever hunted with because of this, and what about all those folks living in those climates using "factory" ammo?? Most of the folks there use factory ammo....
I'm not saying that the ammo wasn't a bit slower, but i don't think changeing the primer will make up for this. Changeing the primer would be to prevent misfires, but i've NEVER had even one center fire shell misfire because of the cold...
And what about that 06 ammo with 215's in it when summer comes back?? I'd be more worried about the higher pressures they will create in the warmer weather!
As for 22 rf ammo in that cold, yes i've noticed a difference in it... In my rifles i would switch to HP's from solids to make up for it. Even on smaller animials, the HP's don't blow up so hard in the extreme cold. 22's shoot lower in the extreme cold and i'm sure it's because of lower velocities...
I spent 15 or 20 days deer hunting, where it went below zero nearly every night on this hunt, without problems...
It was a fly in hunt to a place i hunted often. I was by myself in a small tent, and as always there was no heat... I just loved being out there by myself, no yuppie telephone, and never see another person unrill the plane came back!
DM