The accuracy of chrono readings

[Beethoven]

A gun I use was chrono'd at 355fps at the repair shop after it was mended. However, on site it was chrono'd at 365fps. The BBs were 0.20s on both occasions.

So I wonder whether such disparities are common and what might account for them when they occur.

 

[RR01]

Yes, chrono readings can differ by quite a bit. I've checked previously with my own chrono and had readings on one rifle that were 20FPS higher than a site chrono and a second rifle that chrono'd within about 5FPS on both. A lot can depend on the weather and also if the rifle was unused or had been fired a few times before testing, as the seals could have expanded and created slightly better compression. Even testing one rifle on two separate site chronos gave readings that differed by about 5%.

 

[NickM]

Yes they are quite common. Infact they can end up being much greater in my experience.

I checked a gun with two different Chrono's at a site once and there was over 100fps difference.

There can be many reasons for the difference in FPS reading, there could have been issues with the gun, or any number of issues with the chrono itself including low batteries giving artificially low readings. Chrono's becoming damaged during use, for example bbs striking the sensors.

 

[Shizbazki]

Yes it happens, and the vary wildly with no known international standard or definition guiding chronograph makers, well none that i have seen in the Chronographs made for airsoft anyway.

My main Airsoft shop currently uses the XCoreTech X3200 (and its newer version), my main site as well as several other use use the same Chronograph so i bought one of the exact make and model in order to try and minimise deviances but there is always some.

 

[Aunty Pasty]

Unless the chrono's undergo calibration there will always be a degree of variance. They may be calibrated to a certain tolerance as they leave the factory but they will drift a bit over time.

 

[Sacarathe]

Light levels have an effect, unless two chronographs were side-by-side it's silly to discuss comparative accuracy.

 

[jcheeseright]

A chrono is only as good as the calibration it's been through, 99% of Airsoft sites don't calibrate their chronos at all. Some places use ancient paintball chronos which may as well be random number generators!

Hopefully when the PCB passes and defines a legal limit for Airsoft guns insurers will insist on a calibrated chrono for every site.