Even though you aren't seeing pressure signs at 25F, I'd expect some to show up if you shot that load in 90F weather. The CCI-BR2 is a great primer, one of the reasons it's so good is that its mild. Mild primers and cold weather don't mix well. You could work up a load with another primer for cold weather or keep the cartridges a little warmer.
First thing I'd do is simply put a handwarmer (one of those disposable kind) in the ammo box so it just breaks the chill.
Second thing I'd do (seeing the group is horizontally strung), I'd make sure your shoulder and cheek pressure are very consistent and shoot another couple groups.
As far as other primers, This link has a nice list of relative primer strengths.
Primer Testing Reference
If you can find a 100 Remington 9 1/2 Large Rifle primers (not the magnums) they are a little bit hotter than the CCI-BR2's, but nothing like the magnum primers. Make sure to work up your load from well below maximum.
Hope that helped,