Nick, how many rounds did you chrono at each charge weight? If only one, try measuring 5 of them at one charge and note the spread (SD).
It could be your 100'/s drop is within the margin of error for that load/barrel/brass/bullet/charge/powder/temperature, etc.

+1 for the LabRadar. It's fantastic and you can get an ap for your phone to control it with. And you don't have to worry about hitting any sky screens.
Only problem I have had so far with ours is in measuring some Winchester generic .22-250 50 grainers. I blew a dozen rounds before I realized the bullet
was going faster than the LabRadar can READ! (3900'/s)