I have a fx impact that will not hold a Zero. My first 5 shots are a 2" group from the shots I made the night before. After those first 5 it will settle down and shoot a 1/4" group at 50yds but not the same zero that I left it at the day before. I know with my high caliber rifles I need to be sensitive with how fast I shoot to make sure I don't heat up the barrel. Do I need to do the same thing with an air gun? Or is there another reason my gun is reacting like this?