ORIGINAL: daven
100 feet easily, normally closer to 200 feet.
The cheap guns make you feel completely unsafe trying to get a reading. I will say that I would still like to be further away, but the Stalker Pro is about the cheapest gun that I'll hold trying to get a reading.
I hear you Daven,
I owned the cheapy Bushnell Speedster and you had to be 20-30 feet away (i.e. in the middle of the runway during a low high-speed pass) to get a reading. But it was an $80 gun and it did clock my Diamond Dust at 123 MPH.
What speeds are you seeing on your Q-40s??