FT Blog - Chronographs
- 1 Comments
- Last updated: 21/02/2018
If standing shots are the most dreaded on an FT course, what’s the second? I’d say it’s the chronograph lane! While unfortunately you don’t always see a chronograph in use at regional events, there is always one at the National BFTA shoots. It has been the bone of contention for years with some shooters, quite rightly so in some cases, but not all! You have travelled hundreds of miles for a big competition and could even be near the end of your 40 or 50 shots with a great score, then ‘computer says no!’ You get three chances to be under the legal limit, but if you fail, you are out! Of course, it’s never really the shooter’s gun, it’s the BFTA chronoafter all, they checked their gun on their mate’s chrono and there lies the problem!
Chronographs are precision pieces of kit. Most are very good at reading the speed of a pellet and thus giving your power depending on weight. Given most Field Target shooters use 8.4-grains from Air Arms or JSB, that gives us about 800 fps as a legal limit, or 795 at a BFTA event, where a 5 fps safety margin is in use. However, chronographs must be set up and used correctly.
Battery power is one of the first things to send chrono readings haywire, so always make sure if mobile, batteries are fresh. Ideally, a chrono should always be used with mains power, but that’s not usually feasible in a wood! Light can be a major issue too. Indeed, I have seen Skan chrono readings alter by over 20 fps in the field, all due to a cloud blocking the sun and thus a change in light levels. Some won’t read at all if there is not enough light, which in a wood, is often the case! So ideally, constant light is needed. Saying that, the new Air Chrono and indeed the humble Combro seem to be pretty flexible on light levels.
The one thing I have found from controlled testing, is that the angle that the gun/pellet is fired at over the chrono, can have a massive effect. Both the chrono and the gun should be level with each other and in line. As little as a 5° left to right or vice versa angle on a level set up has seen massive deviations in average results; again, well over 20 fps just by being a little bit out! So, it’s no wonder we see some strange results in the field. Same for ‘distance from muzzle to chrono’- where some cope with the muzzle blast ok, so the end of the barrel close to the sensors is not an issue. Some however don’t. At the BFTA Inters in 2016, a Steyr user was horrified to see his gun record an FAC 810 fps on the first and second shots. For the third, I made him move his barrel back from three to about eight inches from the chrono. 785 fps for the next three shots, proved all was OK with the gun and that it was all about the set up. Thus, ideally all chronographs should be used with some sort of Jig, so consistency is achieved, otherwise you really are in lottery-land with some machines.
Personally, I got lucky with the humble Combro Cb645 ( http://www.chronoscopes. com/ ). I have tested it against a calibrated and controlled Gunsmith’s chronograph, and it was within 2 fps consistently. It’s easy to use in the field, and for £45, there really is nothing better. Same for the Air Chrono we used at the World FT Championships in Wales this year. These have proved very consistent, when the gun is set up correctly for them!
Having gone to the trouble to set your chronograph up correctly, there is little point in looking at the readings unless you know for sure your pellets weight. Yes, they are all supposed to be 8.44-grains in a tin of JSB Exacts, but again a decent set of scales will soon show 8.2 to 8.6 is common in a good batch and in a bad one I have Had 7.9 to 8.9 in the same tin! So, a decent set of scales such as ‘On Balance Ct – 250’ do a great job for less than £50. The test of a good scale is to put the same pellet on three times, you should get the same result. Not many cheap scales can manage that!
Last thing, once you have set the power with one batch of Exacts, don’t presume the next batch is the same! I have two batches of JSB Exacts, both 8.4-grains and both labelled as Die 46, but they have different manufacturing dates. There is a 20 fps difference between these two, so I have go faster ones and slug pace from the same pellet! Remember, it’s your responsibility as the gun owner to make sure you are legal, so do as good and accurate a job of it as you can, and hopefully you won’t be disqualified after all those miles!