Simon Everett discusses how to chrono your rifle and advises on which type is best for you
It all depends on what exactly you want to get from your chrono (to clarify: a chronoscope displays the result as figures on a screen; a chronograph shows the results as a print-out).
The most basic chrono for airguns is the Combro cb-625, which is attached by a hollowed mounting bar to the barrel of the airgun and aligned with the exit from the muzzle. The pellet is then shot over the sensors which sit a few centimetres apart.
The Combro is accurate but liable to being shot by accident – just ask anyone who has ever owned one! Spares are available and the item can be easily repaired by an expert.
The Skan is the popular choice of RFDs with many clubs, and is used to determine muzzle velocity from all the stock or to check competitors’ guns. It is regarded as the industry standard but again is only of use at limited range, from the muzzle out to maybe 10 yards.
The Skan is sophisticated and can self-calibrate with the sensors housed within its tough, steel protective housing. The item also collects the fired ammo in a strong pellet trap and so can be safely used in a confined space; be aware it does require mains electricity to power it, however.
For collating the velocity at range in our pellet tests we use a ‘sky screen’ type and ensure the sensors are set further apart to allow for maximum accuracy.
Various makes of sky screen chrono are available – I use the Caldwell Ballistics Precision, which comes complete with red LED lighting for use under difficult lighting conditions.
If all you want to do is measure the muzzle velocity then the Combro will prove perfectly adequate. On the other hand, if you want to carry out more detailed ballistic research and gather down range data you will need one of the sky screen types to shoot over at long range.
How to set up a Chrony F-1
Measuring muzzle velocity is the most common use for a chrono, and the Chrony F-1 is one of the most widely available models.
1. Unfold and extend
The F-1 needs to be unfolded before it can be used. Make sure you extend it the whole way otherwise the reading across the sensors won’t be totally accurate. It’s powered by a single battery, which should be disconnected after use to prevent it discharging.
2. Use a tripod
You can place the device on a table or other type of rest, but it’s much easier to use a camera tripod to adjust height and angle, ensuring the chrono is perfectly lined up to record your shots. Try not to shoot your chrono! Eye protection is a very good idea, too.
3. Consider a sky screen
Chronos can be used both indoors and outside, but can be fickle if the lighting’s not exactly right. A sky screen can be used here, but they’re a bit tricky to set up and aren’t always necessary. Take a shot without one first and see if you get a valid reading.