How to mount your acoustic chronograph

The SuperChrono is an extremely simple measurement system to use

Provided that the projectile moves at a supersonic speed, you will get a reliable and repetitive reading of the speed of the latter. Light and atmospheric conditions have no influence on the measurement. The term “supersonic” means that the bullet will have to be propelled faster than the approximate speed of 343 m/s. When the projectile reaches this speed, it generates a shock wave that comes into contact with the two acoustic receivers. The speed is calculated on the basis of the time taken by the wave when it activates the first receiver and then the second which closes the circuit.

The maximum detection area is included in a window 80 cm wide by 130 cm high. The accuracy of this reading is identical regardless of the place of passage of the projectile in the defined zone. The illustration clearly shows the shape of the detection window.

To get started

Safety rules are essential and must be respected before any use. You are shooting in a bullet trap, you have unloaded the weapon, removed the lock, secured the elements before installing the chronograph.

The chronograph is powered by four AA batteries. To access the location, turn the chronograph upside down and use the supplied allen key to open the protective cover of the compartment. Install the batteries, close the cover and screw it back on. Install the chronograph on a photo tripod equipped with a fixing system for cameras. Turn on the chronograph.

Configuration

To obtain reliable speed measurements, you will have to orient the device using the sighting organs fixed on the latter. You will have to align the chronograph, the line of sight of the weapon (path of the bullet) and a point of impact on the target. The elements will therefore all be in the same parallel plane.

The procedure is described as follows:

1. The chronograph must be positioned at least 3 meters from the muzzle of the barrel.

2. Make sure that the chronograph is well below the actual trajectory of the projectile and that it points in the direction of the target.

3. Find the height between the actual trajectory of the projectile, the target and the chronograph. For example, using the sighting organs of the chronograph, aim at a point 30 cm lower than the point of actual impact on the target.

4. Aim with the handlebar and the chronograph sight notch just below the point of impact on the target instead of an offset sight.

By respecting these four points, you guarantee the correct operation and reliability of the measurements: the trajectory of the projectile, the axis through the measurement window of the SuperChrono and the target. You can also position the SuperChrono anywhere between your shooting position and the target, on the express condition of always maintaining the parallelism of the different axes.

5. All shots must be fired from the same firing position and always in the same place on the target. This will guarantee the reliability of the measurement simply because the parallel axes will be respected.

Frequently asked questions

Why do we always have to respect the parallels?

– If the elements were not parallel for each of the shots fired, the path of the projectile would be either longer or shorter and therefore the measurement would not be homogeneous within the same series of measurements. This mathematical rule also applies to any of the systems designed with two sensors: acoustic, optical, electromagnetic or radar.

Do I always have to position the chronograph 30cm below the trajectory of the projectile?

– No, the chronograph can be placed at any level below the trajectory: either directly under it up to 130cm lower (see the illustration above on the right indicating the detection window).

The window (detection area) may be smaller than that illustrated when firing with reduced loads or when it is raining or snowing. The display screen is presented at an angle of 15° facing the shooter. If you wanted to read the speed, with each shot fired, you would just have to place the SuperChrono 1m below the trajectory of the projectile but always 3m from the muzzle of the barrel. The readability is then perfect without leaving your shooting position.

Do I always have to place the chronograph directly below the trajectory?

– No, it can be placed 40cm next to the trajectory (see the illustration of the detection window). If you position the device 40cm to the right, you should always keep the same aim with the weapon on the target. If the trajectory was 30cm higher, you would aim with your weapon 30cm lower. The ultimate goal is to always keep the elements in the same parallel plane.

Why is the chronograph positioned at least 3m from the muzzle of the barrel?

– The goal is to prevent the detection of the breath itself. The blast depends of course on the load or the type of ammunition. You will get a correct measurement of a supersonic 22LR ammunition by installing the device close to the muzzle of the barrel. For the speed measurements of the “magnum” ammunition it will be necessary to move the chronograph 4 to 5m away from the muzzle of the barrel.

Does the chronograph have to be pointed in the direction of the targets?

– The SuperChrono detects shots regardless of its position, you install it according to your ease of aiming.

What happens if I position the chronograph very close to the muzzle of the barrel?

– Three things can happen: the recorded speeds would be unrealistic, the display would risk being damaged by the blast, there would be no recording at all because the receivers would be saturated by the shock wave. To avoid the shock wave and the reflection of it, the chronograph will always be positioned further from the muzzle of the barrel than the ground height sensors. That is to say that the distance between the muzzle of the barrel and the chronograph (d) will be greater than the height of the weapon in relation to the unit of measurement (h ) (see the illustration below).

What happens if I aim with the chronograph above the parallel line?

– The read speed will be more important.

What happens if I aim with the chronograph below the parallel line?

– The read speed will be less important.

How can a aiming error influence the reading? r

– The key factors are the distance between the chronograph and the target as well as the speed of the projectile. Loading with an effective speed of 410 m/sec above the receivers and aiming the chronograph 1m too high at 100m will give a reading of 412 m/sec. This deviation will increase with the speed of the projectile. A projectile whose velocity is estimated at 1099 m /sec with the same aiming error will give a reading of 1132 m /sec. The deviation will therefore be 33 m /sec and an accuracy of 97%. If the error was reduced by 33cm, the deviation would be reduced by 11 m/sec and the accuracy would increase to 99%. The sighting organs of the SuperChrono have been designed to guarantee the best positioning of the device and therefore its accuracy. With a little practice you should be able to repeat and use a system whose reliability would be 99.5%. If you are a reloader or a long-range shooter you will find the following spreadsheet very useful (SuperChrono Precision Calculator).

Is the speed calculation affected by the temperature and the variation in the speed of sound?

My SuperChrono comes with a spirit level, for what purpose?

– The spirit level gives you a general idea of the aim. To obtain an accurate aiming, it is imperative to use the aiming devices mounted on the device.