Thread: Chronographs, what's the story

Yesterday I shot some new powder for groups, chrony readings reasonably steady, I mean not to much variation, sorted out a couple of loads that looked interesting and took them back today for a recheck.
Same load , same sort of grouping but readings near 100FPS faster the readings were as reasonably steady as yesterday.

Had the sun shields on both days, sun not out as much yesterday, but still there, but bright today,
then clould cover came over and the speed dropped 50-80-fps for the same grn weight.

Drives me nuts, anybody got a solution.