barrel velocity

I have 28 or so rounds down the pipe in a factory 6.5prc savage tactical. First couple shots hovered 2950....by the end of those first 12 shots it was 2922 (magneto speed)57.7 h1000 Pressure wasnt a problem at all so i bumped to 58.4 first 2 were back up to 2950. By the time i was finished with...