Excellent point from both Briman and oldelkhunter . This is another common issue for POI changing ESPECIALLY when the temps are extreme on the low end. I like to clean the barrel at the range when I'm done, then run it clean and dry with patches. Then fire 2 fouling shots and put it away after it cools. The debris in the barrel gives me a more consistent platform for when I come out later.
Shooting from a consistent condition is the key.
If your first shot is ALWAYS out of a cold and 1 or 2 shot barrel that is clean and dry otherwise it gives you a starting point. Let the barrel then cool completely (couple minutes when it's 30 or below!) before trying to get a second shot in .... it's needed to duplicate the conditions of the first shot. That may be WAY easier than trying to do the upward pressure thing.... especially if it works!