Chronograph Calibration ?

[zooma]

We have an F1 Chrony fitted with the Chrony LED lighting umbrella that we occasionally use on the club range to check the fps of our airguns.

Although not very old, and not used that much (and carefully kept in "mint" condition) we have been happy with the constant results it gives and the results we have taken compare favourably with readings that have been obtained from alternative sources, but it has recently been suggested that perhaps chronographs need to be re-calibrated now and again to ensure that they maintain their accuracy.

I know that there is a requirement for speed cameras to be recalibrated now and again, so I suppose that the same could be said for airgun chronographs too, but does it really make any practical "real life" difference if a well cared for and seldom used good quality system such as ours is not re-calibrated from time to time?

We use our Chrony to check for any changes in fps over a range of consecutive shots so we can see how consistently any airgun we choose to test are shooting. These figures can then be converted to find out the ft/lbs when used with the weight of the pellet (in grains) if we wanted to check the power too.

A well established mathematical formulae exists for this conversion to ft/lbs and is also available online (and with some phone apps) for a quick reference. This quick reference is only a guide but we can double check the results "long-hand" if we wanted to be certain or if any result comes close to giving a higher power rating than we would be "uncomfortable" to use on our club range as we will not allow any air rifle over 12 ft/lbs and no air pistol over 6 ft/lbs to be used.

Most target grade match pistols and match rifles fall well below the legal maximum permitted legal limits of 6 and 12 ft/lbs respectively, but some of the sporting rifles come a lot closer and so we would always want to check them to make sure that they were "legal" before allowing them to be used on our club range.

I believe that the results that we obtain from our Chrony system are accurate enough to use as a reliable guide to help us check how consistently a regulator is working on a PCP or CO2 air pistol or air rifle and can also be used to check how consistently any other type of airgun ( spring powered or SSP) is shooting too.

To ensure good results, we never look at the result of just one shot, but aways take a string of at least 10 shots with one known pellet type and then repeat the test with further 10 shot strings with at least two other different known brands of pellets to get a fair spread of readings that the airgun is capable of achieving. We also take a few shots before measuring the fps (especially with springers) to allow the rifle to "settle" as we have noticed that sometimes the first few shots can be more variable.

Until now we have always been happy to consider the results that we take to be more than good enough to identify any airgun that is over the legal limit accurately enough to prevent it being used in our club if we can see it has more power than we are legally entitled to use under the current UK law.

If our results identify an airgun as being too powerful (ref above) I would also advise the owner/user not to shoot it without suitable firearms certification outside of the club range either as it could be considered to be an "illegal" airgun and there is a possibility that the airgun could be seized and the holder/owner/user could face prosecution under the current firearms laws if it were to be tested by an enforcement agency before it had been adjusted to shoot with less power and within the legal limits.

I understand that if a prosecution should be made that the enforcement agency engaged by the police to support the charge would need to be able to prove that their equipment had been calibrated recently enough to pas as "fit for purpose", but I believe that to be unnecessary when we only use our Chrony to assist with accuracy and pellet speed testing or to identify and advise if an airgun produced more power than our current law permits us to use without appropriate certification.