Not your usual calculator

Kestrels have been seen as the premier tool for ballistics calculation in the field for quite some time. The 5700 was released a few years ago with Applied Ballistics (AB) and has yet to be superseded by an in-house variant, although Kestrel has worked with a few manufacturers to produce branded versions. However, the 4DOF is a little different.

 

What is 4DOF?

 

As well as all the atmospheric variables the Kestrel measures alongside individual gun profile builds to compensate for barrel twist rate, line of sight above bore etc., one of the key variables required in any ballistic solution is the ballistic coefficient (BC) of the bullet in use. Common G1 and G7 BCs are measured, rather than calculated. They are a proportional representation of the bullet in use relative to a ‘standard projectile’, and the subject certainly cannot be covered in a 2-page article. Essentially, the G1 was based on the shape of the older, flat-based, short-nosed, tangent ogive bullets. The G7 is focused towards the modern, secant ogive, boat-tailed match bullets that we use to extend the range of our rifle/ammunition combination.

 

Why is it different?

 

Hornady’s 4DOF ballistic calculator works differently and frankly, in a mathematically more complex way, but all the number crunching is handled either by the kestrel or your smartphone, for which an app is also available. 4DOF uses the drag coefficient of the bullet, which is different to the BC. The drag coefficient is calculated from precise modelling of the bullet shape and includes mass distribution. The DOF stands for ‘degrees of freedom’ and as well as windage, elevation, and range, the fourth dimension included is the angular movement/yaw of the bullet in flight. 4DOF is the first tool able to accurately calculate the vertical shift of a bullet as it encounters a crosswind, something referred to as ‘Aerodynamic Jump’. To simplify this, imagine a bullet is like a wind vane that aligns itself to the wind. Its vertical and lateral yaw around the centre of gravity (from the crosswind), play an important part, so the calculation of the shape and mass distribution, as well as spin rate, contribute significantly towards calculating this varying yaw to refine your shot solutions, including the angle of attack throughout its flight from muzzle to target.

 

Is it better?

 

So, why is this totally alternative method better? Well, Hornady thinks that with modern computing, using a comparison of your bullet to a ‘standard projectile’, rather than using an exact projectile model, is a little outdated. The drag coefficient is far more predictable. Ballistic coefficients are calculated from the velocity degradation curve of the projectile in flight by using Doppler radars, and the ballistic coefficient can alter as the velocity changes, whereas a drag curve is specific to each projectile and is directly related to its trajectory. Over 400 variables are incorporated in the 4DOF calculations.

 

App option

 

4DOF is available as a free smartphone app, with no need to pay a penny unless you choose to add one or two of the single-digit cost add-ons. Yet, when incorporated with Kestrel’s 5700 Ballistics Weather Meter, it’s a tough, dustproof, waterproof (IP67), and shockproof tool made to military (MIL-STD-810G) standards, including all the atmospherics your phone can’t measure. It’s all powered by a single lithium AA battery, with large buttons and a backlight. The windspeed impellor is protected with a folding cap and the other delicate external sensors are physically recessed to avoid snagging. You can navigate the menus with gloves on and personally, I think the smartphone is used as a crutch to make a lot of products look versatile, yet when they all rely on it, a single drained battery is game over for all of them. The key ability of the kestrel is that once set up, you can point it at your target, click to allocate a target bearing, enter the range to target, and then with the wind reading live, turn it into the predominant wind direction/bearing to assess the required windage correction. I cannot stress enough that this is not a perfect solution, as wind strength varies constantly, and you are only measuring speed and direction at a single location, but it is a huge help to get started with.

The Kestrel can handle three complete rifle/ballistic 4DOF profiles and whichever you chose, is running in real-time and giving shot solution updates second by second. If you pair the Kestrel with the automatic wind vane, it self-aligns. Similarly, if paired with the heads-up display, it provides a superb range assistant for long range shooting. The Kestrel does have Bluetooth connectivity if you want to link it to your smartphone app, which can make data entry for overall profile builds a little faster, however, it is not mandatory.

 

Limitations

 

The 4DOF version will only store three rifle profiles, rather than the 30 of the AB version. It also only runs a single target versus 30 stages/10 targets of the AB, but it is £170 cheaper. It still includes truing capabilities using ‘Axial form factor’, plus can still operate with G1 and G7 BCs. Hornady is constantly adding bullets to their 4DOF library from many manufacturers, although cannot compensate for bullets that use polymer tips that soften/deform in flight.

 

Conclusion

 

From a mathematical point of view, I can see how the 4DOF system is technically incredibly astute, but the additional processing power requirement does restrict the versatility of the 5700 a little, yet this is offset by a lower cost. The system is undoubtedly very modern and well-engineered, but a lot of shooters have become accustomed to the intricacies of G7 calculations and know how to true them up, so will they want to learn a new language? Especially when reading the wind between you and the target is still a massive variable. However, as a new user, it certainly makes a lot of sense, and it proved just as accurate and easier to use. I suspect that 4DOF will be very beneficial to extreme-range shooters, where the calculation detail will become most visible.

 

Specifications

 

Features three guns 1 target, axial form factor calibration guide, Coriolis, corrects wind temperature, altitude, easy mode, G1/G7 drag, gun profile storage, Hornady 4DOF custom bullet file, LiNK, moving target lead calculator, muzzle velocity, temp correction, MV calibration guide, spindrift, target range estimator, target speed estimator, and zero angle.

The atmospheric measurements include altitude (barometric), barometric pressure, compass direction, crosswind, density altitude, dew point temperature, headwind/tailwind, heat stress index, relative humidity, station pressure (absolute pressure), temperature, wet bulb temperature (psychrometric), wind chill, and wind speed/airspeed.