Sounds like the chronograph wasn't working reliably on that day.
When using a Chrony I prefer to use it at night with LED strips on the underside of the skyscreens - eliminates the vagaries of daylight. Much more reliable.
I also shoot one of two ways to make it more stable;
1. Secure the chrono to a concrete block/breeze block with a mini tie-down strap. Put this on the ground and shoot prone - very stable and safe. Or,
2. On top of a concrete shooting bench and shoot from behind the bench with the gun on a tripod. So the chrono is on the bench and the gun on the tripod, not the other way round. Depends of course if the range rules allow this.
I also bought a few silicone rubber feet which come with a peel off sticky side. A few cents at the hardware store. Stick one at the corners and it's even more stable on a concrete bench (on one half only for a folding Chrony).
Plus a cheap spirit level/bubble to make sure it's level to the ground before shooting. A few degrees different to the line of bullet and this lengthens the distance of bullet path between sensors. Gives false lower readings.
12V Light strip and bubble level (EBay).
[ATTACH=CONFIG]16091[/ATTACH]
Rubber feet
[ATTACH=CONFIG]16092[/ATTACH]
Save yourself the angst and invest a few more dollars in getting your chrono more reliable.
To be honest, I use a LabRadar now, but still have the old optical chrony as a backup.
When using a Chrony I prefer to use it at night with LED strips on the underside of the skyscreens - eliminates the vagaries of daylight. Much more reliable.
I also shoot one of two ways to make it more stable;
1. Secure the chrono to a concrete block/breeze block with a mini tie-down strap. Put this on the ground and shoot prone - very stable and safe. Or,
2. On top of a concrete shooting bench and shoot from behind the bench with the gun on a tripod. So the chrono is on the bench and the gun on the tripod, not the other way round. Depends of course if the range rules allow this.
I also bought a few silicone rubber feet which come with a peel off sticky side. A few cents at the hardware store. Stick one at the corners and it's even more stable on a concrete bench (on one half only for a folding Chrony).
Plus a cheap spirit level/bubble to make sure it's level to the ground before shooting. A few degrees different to the line of bullet and this lengthens the distance of bullet path between sensors. Gives false lower readings.
12V Light strip and bubble level (EBay).
[ATTACH=CONFIG]16091[/ATTACH]
Rubber feet
[ATTACH=CONFIG]16092[/ATTACH]
Save yourself the angst and invest a few more dollars in getting your chrono more reliable.
To be honest, I use a LabRadar now, but still have the old optical chrony as a backup.