First Shot after a brake always faster

[Blacktornado]

I have a new FOpen class gun , 300 WSM, I have 120 rounds on it and it happens something very strange. I have a certain experience but it never happened before. I'm fouling my barrel first and then I have five shots groups and between two groups I stop for 4-5 minutes to cool down a little the barrel . The first shot of the new group is always 30fps faster than the others . Others 4 shots are grouping great but the first one not . Very strange . Did you have similar experience ? Thanks

 

[Clancy]

I bet it’s cooking in the chamber while you’re preparing to fire. I don’t ever chamber a round until I’m ready to put it on target.