Is it posible that the firing pin is not operating correctly due to too much oil that when it gets cold doesn't let it function correctly- too much drag due to excessively thick oil vicosity at lower temperatures. The wrong oil at low air temperature has been known to do that in alot of rifles. Try cleaning the trigger and firing pin assembly, then reoil with a light oil say something lick door lock oil for your car( it also has graphite in it to help lub ). I hope this helps with your problem.