Ranch- Would say that something changed in your shot set up, either your omitting something latter or adding in some bad habit in the later groups. Try shooting a group and walk away for 5 minutes and come back and shoot another. And so on for 6 groups or so and see if anything changes. Usually when I see heat effecting bullet spread the results are more profound ( and we are talking a lot of heat) than what you have demonstrated with your shots.
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