Re: primers, powder, outside temperature 300WM
Welcome to the forum,
I'll answer a couple of you questions.
I use non-magnum primers in my 7mm Rem Mag and have never had problems in cold weather using H4831 and RL-22.
I've shot terrific groups with new brass. I once had a load that shot lights out in new brass and just average in once fired. I had to adjust the seating depth and increase the powder a touch to regain the accuracy in fired/resized brass.
If some is good and more is better, then too much is just right.
My mind is a raging torrent, flooded with rivulets of thought, cascading into a waterfall of creative alternatives