Was a new bottle, lot number of Bullseye opened? I tested 3 different powders by volume. New lots have been heavier then the old lots. Using the same measure setting.My last batch of 1000 45 acp went from 5 grains of bullseye to 6 grains around the 600ish round mark
Outgassing of smokeless powders may be the cause. I never mix different lot numbers of the same powder.