By Geoff Smith
Most shooters will have some interest in knowing the velocity at which their bullets are being sent off to the target. This enables an estimation of flight time to the target, which in turn gives an indication of likely bullet drop. This, of course, is critical for being able to hit the target in the right place, especially at longer ranges. Because gravity pulls bullets downwards as they leave the muzzle, we need to know by how much to set our sights over the line of the bore axis.
Measuring a string of consecutive velocities has the further advantage of gauging the consistency of the ammunition. Variability in consecutive velocities will greatly influence grouping capability. Without knowing bullet velocities, we will understand less about why our groups might be larger than expected or away from where we’re aiming. Velocity is also a critical determinant in how much energy our bullets will carry to the target, since energy is proportional to the square of the bullet’s velocity.
The rise of digital electronics has given us several ways of measuring bullet speed during the past few decades, with the most recent (at least for domestic shooters) being the use of radar. The subject of this review is a very convenient portable device that accurately does this by emitting a 120-gigahertz beam of radio waves downrange, then analyses the echo coming back from the bullet’s base to determine velocity. This measurement is then transmitted, using blue tooth technology, to a smart phone or tablet on which an app has been installed.
The unit has been developed and produced by a team of engineers in Germany and Czechia (formerly Czech Republic). It was in what is now Czechia that Austrian physicist Christian Doppler (1803-1853) first came up with the mathematics explaining how the wavelengths of signals change when bounced back from moving objects, some 150 years ago. When a beam of radio waves travelling at the speed of light is bounced back from a receding object, it returns at the same speed, but now with a longer wavelength (much like the ‘red shift’ of receding stars) and this change is what enables the speed of the bullet to be determined.
Weighing in at just 226g, the cylindrical aluminium case is 101mm long and 40mm in diameter. The supplied unit is black while a ‘sand’ coloured alternative is available. Supplied with the tracker is a conical shaped ‘Parabolic Adapter’ that slips on the front and helps focus a stronger signal back to the detector. This increases the overall length to 141mm and weight to 280g. The tracker needs to be located parallel to the barrel, no more than 150mm away, and no more than 600mm behind the muzzle. Some special requirements must be met when using muzzle brakes and firearms that emit large clouds of discharge gases, but this didn’t arise in my tests with handguns and rifles. I did find a certain amount of experimenting is required to find the best means of mounting it, but once done it works very well. Similarly, a bit of learning is necessary to come to grips with the app.
For rifle applications the tracker is most conveniently attached directly to the rifle using Picatinny style mounts where available. Being powered by an internal battery, there are no cables to cause issues and the beam is emitted in precisely the same direction as the bullet, even as the barrel lifts during firing. With handguns it was initially necessary to hold the handgun alongside the tracker mounted on a small tripod and missed shots occurred a few times.
Anybody who has used the older style of photo electric chronograph, which uses ‘sky screens’ will immediately appreciate the ease of use of this unit. There is no careful alignment needed in setting up, or subsequent accidental shooting of screens, as the unit operates entirely behind the muzzle. You simply turn the unit on, open the app, then press the button on the tablet or phone display to connect the two and you can start shooting and recording shots. The app enables the results to be stored and they can also be exported as ‘csv files’ where required. (CSV files are ‘comma separated value’ files such as are used in spreadsheets like Microsoft Excel.)
So, having unpacked and charged the unit via its mini-USB cable, it is then necessary to download the app. This is available at no cost for either Apple or Android devices from the relevant app stores. Once installed on the phone or tablet, having ensured blue tooth is enabled, the tracker is paired to the display unit. In my case, I used an iPhone and I had no problems installing and pairing the two devices. The tracker is turned on by pressing and holding the On/Off button for one second. The indicator is red when starting and when connected it changes to green, with the display showing ‘Connected’. When a shot is fired, the indicator light changes momentarily to blue and the display then shows, and with my iPhone, audibly reads out, the recorded velocity. Each consecutive shot goes into the string, and the average and standard deviation is recorded, stored and displayed immediately. A few seconds is required between each shot.
Bullet velocities up to 1,200 metres per second (or 4,000fps) can be measured and stored in each string. The data from each string remain stored on the phone or tablet and can be exported for use in other programs. For each string, a profile can be generated in which the details of the firearm, barrel length, calibre and load data are recorded. During set up you can request metric or imperial units. Once a profile has been generated, this can be saved and reused with further strings when using the same firearm and ammunition.
On the overview of each string, every shot that is recorded will have a velocity, time and a coloured dot to the left of the shot number. These may be green, orange or red. Green means you will have more than 100 detections, while orange means between 50-100, and red will be less than 50. One of the tests I performed used a CZ .22 rifle with Federal Premium Target ammunition. Of the eight shots that recorded, number eight was coded red, as it only made 13 measurements, while shot five was green and made 175 measurements. If you then go to the ‘Statistics’ screen, you can read off the string velocities as minimum, maximum, average and standard deviation.
I downloaded and printed the 17-page pdf ‘Quick Reference Guide’ from the web site (speedtracker.tech/services) and found this to be very useful in making sense of the app and how to use the device itself. For my tests, I firstly used the little tripod that was included in the material sent for review, and while this was useful, I’m certain that muzzle lift led to several missed readings both from handguns and from several larger rifles. I also attempted unsuccessfully to clock speeds from an air pistol. The best results were obtained by attaching a small Picatinny-style clamp to the barrel of several rifles some distance back from the muzzle. This gave immediate success on virtually every shot. I used a CZ 452 .22 rifle and a Sako Vixen L461 .222 rifle with a variety of different loads.
After this I decided to mount the tracker using the same clamp under the 300mm barrel of my Taurus Model 66 .357 magnum revolver and see how many shots recorded during a 40-shot silhouette match. The extra weight meant it was somewhat clumsy holding the gun in a two-handed, offhand grip, but the experiment worked. Every shot registered and as a bonus I confirmed a previous suspicion about the propellant I had been using. You get to know when the velocity of shots vary, and so when a shot that feels soft is fired and the impact is unreasonably low or vice versa, you begin to think something is wrong. My test confirmed that a load of five grains of APS 450, which should have produced a velocity near 1000fps with Tigershark 158gr HP bullets, averaged 892fps, with a standard deviation of 45fps. The individual velocities varied from 968fps right down to 755fps, which explains a lot! This would account for about 13 inches of variation in the vertical plane at the 100m mark. Why this lot of powder should perform so poorly compared with earlier batches, I have no idea.
The Speedtracker Mach 4 chronograph is a very well-designed, convenient and easy-to-use device, requiring only a smart phone or tablet on which to record the data and for long range rifle shooters it will be of particular use in setting up the rifles and developing loads.
The review unit was loaned by Speedtracker Australia whose web site (speedtracker.com.au) gives a lot more information. The retail price for the tracker and the parabolic focussing attachment is $1695, at the time of writing. For more information, please contact the suppliers directly.