Originally Posted by uv_halo
Did you already consider where the chrono's were pointing (what was in the back ground), how high up from the ground they are, your (or the refs ability) to position the chrono correctly.
Even something like marker placement can lead to significant variations. Both the big red and, the grey RadarChron need to be 1" back behind the muzzle, with the barrel resting on the bumpers provided and angled correctly (gray model needs to be held perpendicular to the barrel, while the big red needs to be placed level, and the barrel kept level).
As near as I can figure, I had the chronos properly positioned. Heck, that was the first thing I did when I got such odd numbers, was to check my placement... I expect a little bit of FPS creep from day to day, but 50 FPS seemed like an awful big change for what I thought were very minimal changes in my setup. There was no offending interference; out in the open with no metal or structures nearby. It might just be a mystery I'll never figure out. That's why we chrono every day!
Usually I'm pretty anal about chronoing. Definitely after any change i.e. different brand of paint, new barrel, etc. And sometimes, during the day, just because. The only thing I can account for is that one of these was off some way...