People are completely geared up to think that bigger is better and when it comes to primers, bigger is better always wins the argument. Not because anyone has proven that magnums work better, but because of the solid argument of virtual no difference in cost, so why not use the biggest primers?
From my own experience with shooting in severe cold, I concluded there was no difference in primers igniting the powder, whether in normal, or extreme cold weather.
My best argument for this dates back to when Canadian Industries Ltd. made ammunition headstamped D.C.Co., which they knew would be used to keep many northern Canadian rural families with winter food, by killing big game in very severe cold weather. The same normal primer was used for all seasons in their ammunition.
However, every hunter in those conditions knew they had to use kerosene to thoroughly clean all oil from the firing mechanisms of their rifles in the fall, then leave them dry all winter. Every time I hear of someone shooting in what he considers cold weather and has some misfires which he blames on weak primers, I will bet the farm the problem is stiff oil around the firing pin.
The cold weather test that Boomer made to test primers virtually proved that it made no difference, even with ball powder in very large calibre rifles, whether the primer was standard or magnum. Any differences, one way or the other, were well within the realm of standard tolerances, including the chronograph.