It is interesting to note that 2 groove rifling was a wartime expedient and was not used, to my knowledge,either pre or post war. I have also noted greater variation in bore diameter in the two groove barrels. Accuracy in a tight bore appears to be similar for most purposes. However, when accuracy starts to degrade it appears to occur much more radidly in the two groove barrels. It is my general impression that the two groove barrels tend to heat up more rapidly although I have seen no emperical evidence to this