Tried something similar a few years back while testing BC on Francois old S400. Still have the data in my note book.
Got the following with AA fields 10 shots at each distance:
1m 776 - 787 avg 782
20m 701 - 707 avg 703
30m 662 - 674 avg 668
40m 630 - 651 avg 640
Groupings if I recall were not great over 20m.
Had to re-shoot the 40 meter test when things went pear shaped. Got readings of 300 to 1200 feet per sec.
Could not understand it until I noticed a reading pop up without taking a shot. The insects had taken a liking to the white paper target I had placed behind the chrono as an aiming point. They were flying threw the sensors causing mayhem.