I was going to suggest chrono and sun angle. I had the same thing happen to me two days ago. I set up at dawn. Range faces north. At first no readings then around 7:30 I got some...the pet load for my 30" barreled 7 rem mag with moly'ed 140 accubond is 3400 fps @ 80 degrees. I got readings of 3300 FPS!!!! Another hour later it was up to 3375 which would be right for 55 degrees.
