Common problem in the summertime if shooting too rapid! It takes very little to overheat a ML barrel.... even less to overheat the soft, extruded steel of a Traditions or CVA rifle.

I'll bet the bullet was getting more difficult to load too! Make sure you are using a bore brush swabbing & did you go downrange to see how many petals were missing from each blue plastic sabot? If two or more petals were missing, that could of been the majority reason for your inaccuracies.