Frequently Asked Questions

4DOF is a ballistics engine created by Hornady for their bullets as well as other common long range bullets made by other manufacturers. The 4DOF solver utilizes a modified point mass solution which models bullet flight in 4 degrees of freedom to provide incredibly accurate trajectories to extremely long ranges. The software does not use Ballistic Coefficients (BC), but instead utilizes Drag Coefficient versus Mach number data measured with a Doppler radar for each projectile. While the 4DOF solver does not use traditional ballistic coefficient numbers, the Kestrel 5700 with Hornady 4DOF also includes a traditional G1 & G7 ballistics engine for use with bullets which don’t have a 4DOF bullet file available.

Due to differences in barrel machining, muzzle breaks, propellants and other factors, when the same bullet is fired from different rifles there will be a slight difference in the drag the bullet will experience. The Hornady 4DOF solver assumes the bullet will be fired from an "average" barrel but in reality your rifle may impact the bullet slightly differently. To account for any differences the Axial Form Factor value can be modified to align the output from the solver to what your bullet is experiencing. By firing at a known target and adjusting the Axial Form Factor value till the predicted solution matches real world results, you can calibrate the solver to match your rifle and bullet and deliver even more accurate firing solutions. Axial Form Factor can be calibrated using a target anywhere from 300 to 800 yards away and impacts the solution through the supersonic, transonic, and subsonic flight of the bullet.

Zero range is the distance from the muzzle to where a straight line following the axis of your scope crosses the flight path of the bullet. The scope is typically adjusted so this crossing point happens at 100yds but can be set further out. Because the flight path of the bullet can be impacted by changes in environmental conditions, the distance to that crossing point can vary with altitude or changes in the weather, notably if longer distance zero ranges are used. Zero Angle on the other hand is a measure of the angle between the straight line following the axis of the scope and the straight line following the axis of the rifle barrel. This angle is very small and would be difficult to measure directly but the 4DOF ballistics engine can find the angle when provided with environmental data and bullet impact location. Once the solver knows the Zero Angle between your rifle and scope a very accurate solution can be provided regardless of how long the zero range is or how much the weather changes. Read more about the Hornady 4DOF ballistics engine.

Zero Angle is available but it is not the default option. To find Zero Angle in your Kestrel, enter the gun menu and scroll down to Zero Range (ZR) and press the center button. In the Rifle Zero sub menu, highlight Zero Range and toggle left or right. Zero Range will change to Zero Angle and a Calibrate Zero Angle command will appear below it. Selecting Cal Zero Angle will open the Zero Angle Calculator tool.

In the Kestrel LiNK Ballistics app, enter the Gun Profile Editor where you build profiles and tap the Zero Range field name in yellow. In the pop up you will see an option to switch to use Zero Angle.

Because not all laser rangefinder manufacturers use the Kestrel Ballistics Bluetooth Protocol to talk to a Kestrel, the Hornady Kestrel cannot communicate with some rangefinders which can talk to our existing ballistics meters. Check out this page to find the latest updates on which will connect with a Kestrel 4DOF unit: 3rd Party Devices

If you have a laser rangefinder with Bluetooth LE which you would like to have communicate with one of our Kestrel meters please contact the manufacturer and ask them to implement the Kestrel Ballistics Protocol in their rangefinder.

When calculating Zero Angle, the Hornady Kestrel asks for the distance to the Zero Target. This distance can be any distance you want but you’ll want to pick a distance where you’ll be able to accurately measure the distance between your point of aim and average point of impact with no elevation dialed or held when shooting. 100 yards or meters is a convenient distance and may be close to where your rifle is already zeroed.

Note: Just because your shooting range says a berm is at 100 yards, you should still confirm that distance with an accurate laser rangefinder or 100 yard tape measure.

After entering the Zero Angle sub menu, select Cal Zero Angle and then follow the prompts to enter the required data for your shooting environment and target. When shooting at your zero target, make sure your scope turrets are dialed to zero elevation, don’t hold any elevation in your reticle and place the cross-hairs directly on the target (point of aim). After firing enough shots to be confident of your average point of impact, measure the distance between your point of aim and average point of impact. Enter this value in the Cal Zero Angle calculator field asking for the Impact Height at Target, (impacts above the point of aim are positive and below are negative). After calculating the Zero Angle, press Exit and when prompted, accept the Zero Angle value.

The Kestrel LiNK Ballistics app works with all of our Kestrel Ballistics meters. It recognizes the exact meter that you are currently connecting and changes to match that Kestrel.

Please see this guidance:

Kestrel 5700 with Hornady 4DOF Downloads

How to Calculate your Axial Form Factor   (Size: 111.2 KB)

Guidance on how to properly adjust your Axial Form Factor

A bullet file is the exact physical model of the projectile that includes the bullet's mass properties, aerodynamic moments and Doppler Radar determined drag coefficients. By having the exact shape and mass distribution of the bullet along with the aerodynamic moments and drag coefficients for that specific bullet, 4DOF can accurately model the dynamic flight characteristics and provide an incredibly accurate trajectory solution. This exact modeling of the projectile allows us to predict drop, wind drift, projectile Gyroscopic Stability Factor (Sg) as a function of range, yaw of repose and corresponding prediction of spin drift, aerodynamic jump due to a cross wind, and limit cycle yaw at extended ranges due to Magnus effects.

Please see this guide:

Kestrel 5700 with Hornady 4DOF Downloads

How to Connect a Kestrel 5700 with Hornady 4DOF to Kestrel LiNK Ballistics App   (Size: 227.9 KB)

Quick guide on connecting a Kestrel 5700 with Hornady 4DOF to the Kestrel LiNK Ballistics App

Please see this guide:

Kestrel 5700 with Hornady 4DOF Downloads

How to Create and Transfer Bullet Files with Kestrel LiNK Ballistics App   (Size: 444.1 KB)

Quick tutorial on how to create and transfer gun profiles for Kestrel Hornady 5700 4DOF units