ok, everyone else has thrown in all the suggestions I was going to say......so I am thinking outside the box here and throwing something else out. Heat from 1st shot to 2nd shouldnt affect anything, maybe 4th, 5th or 6th but not from #1 to #2. However I had a problem where one of my scopes was mounted too close to the barrel. I had the wrong rings. At ambient temp you could see light (barely) between the scope and barrel, but after the first shot it closed up. Im just throwing a different suggestion in the mix. Could the scope be being touched and moved up by the barrel??