# Instructions

The essential gun-related inputs are explained below. Before you begin, the inputs you must have at your disposal include:

- Bullet Manufacturer
- Name
- Caliber and Weight
- Muzzle Velocity
- Sight Height
- Barrel Twist
- Axial Form Factor

## Inputs

**Units:**

Choose from either Standard or Metric (affects **ALL** inputs and outputs).

**Standard units**are SAE units (inches, yards, etc.)**Metric**(centimeters, meters, etc.)

**Output Units:**

Choose from **MOA** (Minutes Of Angle, this is true moa 1.047” at 100 yards), **MRADS** (Milliradians),** Inches** or **Centimeters**.

**Choose Bullet:**

Pick a projectile from the projectile library. When you do this you are picking a file that contains all the projectile specific information needed to run the 4DOF^{®} simulation. You DO NOT specify a BC (this calculator uses a Drag Coefficient and doesn’t use BC). More information on our FAQ page.

**Temperature Sensitivity Factor (TSF):**

This option allows 4DOF^{®} to compensate for changes in muzzle velocity because of temperature changes. This is an optional input and does not have to be used.

If selected the input allows the use of a **Selected Powder TSF** or a **Custom TSF**. Either input will also ask for a Baseline Temperature. The Baseline Temperature is the temperature at which a known muzzle velocity was produced. This known muzzle velocity is also the velocity that should be input in the Muzzle Velocity required below. The 4DOF^{®} will now automatically compensate for the performance difference between the known baseline muzzle velocity and the conditions that exist at the time of firing. For more details please consult the Hornady® 4DOF^{®} Ballistic Calculator Technical Document.

**Muzzle Velocity:**

Actual muzzle velocity corrected to the muzzle from the chronograph location.

**Max Range:**

The furthest distance you want to be represented in your trajectory output.

**Interval:**

Output solution distance i.e. trajectory information for 100, 150, 200 yds would be an interval of 50. The calculator allows a range interval as small as 1 yard or 1 meter.

**Zero Range:**

Exact distance from muzzle to target where the rifle was zeroed. Be as precise as possible in order to get the best results.

**Zero Angle:**

This will automatically be computed and displayed in the 4DOF^{®} output as Zero Angle. After running 4DOF^{®} for a known zero distance and atmospheric conditions, Zero Angle can be input rather than Zero Range and 4DOF^{®} will output what the trajectory is and the distance zero crossing no matter what the atmospheric conditions or altitude.

**Sight Height:**

Exact height of the CENTER of the scope to the CENTER of the bore of the rifle. Again, be as precise as possible in order to get the best results.

**Shooting Angle:**

Line of sight angle relative to level ground.

**Wind Angle:**

Wind relative to the projectile headwind = 0 degrees, from the right = 90 degrees, from the left = 270 degrees, etc.

**Altitude:**

Input the elevation at the firing location in either feet or meters above sea level.

**Pressure: **

In inches or millimeters of mercury.

**This is station pressure, from a Kestrel™ or similar – use of National Weather Service [type] data for the area will not be accurate nor is it recommended for use.**

**Temperature:**

In degrees Fahrenheit or Celsius.

**Humidity:**

As a %.

**It is necessary with the Hornady 4DOF**^{®} Ballistic Calculator to specify the altitude and atmospheric conditions (either known from a pressure at altitude table or attained from a Kestrel™ or similar device) at the firing location in order for the calculator to accurately predict trajectories. Rather than assuming a fixed atmospheric condition, the calculator calculates an altitude-based atmosphere dependent on the input conditions and allows for the atmosphere to change in air density as the projectile climbs or descends along its line of flight.

**Barrel Twist:**

In inches or centimeters per turn, depending on which units have been selected.

**Axial Form Factor:**

Allows the shooter to adjust the average Drag Coefficient (Cd) curve for each projectile listed in the calculator, higher or lower, to match his/her specific barrel, propellant, twist rate, rifling, muzzle brake, etc.

.- Insert all other input information
- Leave
**Axial Form Factor**input at the standard (1.0) - Shoot your rifle, then measure the elevation deviation, as accurately as possible, from the trajectory solution given in the calculator to that of what was shot. Shoot at the farthest distance you can without compromising the ability to get an accurate point of aim/point of impact results in order to measure deviation.
- Adjust the
**Axial Form Factor**number either up to drop, or down to elevate the trajectory given in the calculator until it matches the trajectory you shot.- If impacts are HIGHER than the predicted trajectory, DECREASE the
**Axial Form Factor**number until the predicted and actual trajectory match. - If impacts are LOWER than the predicted trajectory, INCREASE the
**Axial Form Factor**number until the predicted and actual trajectory match.

- If impacts are HIGHER than the predicted trajectory, DECREASE the
- Keep the
**Axial Form Factor**number for the gun, bullet, and load you shot somewhere for safe keeping. This number is specific to that rifle and load and should be used to calculate accurate trajectory information anytime you use the Hornady 4DOF^{®}Ballistic Calculator.

For more information on **Axial Form Factor**, please see the Hornady 4DOF^{®} Ballistic Calculator.

## Outputs

The Hornady 4DOF^{®} Ballistic Calculator allows you to select the outputs you want.

#### Default Outputs

**Range:**

Your inputs in either STANDARD or METRIC (Yards or Meters) with Max Range, Interval etc.

**Total Come Up:**

Shooting solution – what the shooter needs to dial or hold over on his/her scope. This takes all elevation-related computations into consideration to provide your shooting solution.

**Total Windage:**

Shooting solution – what the shooter needs to dial or hold off on his/her scope. This takes all windage-related computations into consideration to provide your shooting solution.

**Gyroscopic Stability:**

Calculated using the rifle’s twist rate, bullet physical characteristics, the center of gravity, aerodynamic properties, and velocity. The number increases as the bullet moves downrange. To attain acceptable aerodynamic performance, we recommend a muzzle **Gyroscopic Stability (Sg)** above 1.4.

**Gyroscopic Stability Factor (Sg)** at the muzzle is highlighted in yellow. The barrel twist, velocity, and air density will determine the muzzle **Sg** along with other projectile properties included in the projectile file. Doppler radar data has shown that the maximum aerodynamic performance is attained, at higher velocities, with a projectile **Sg** of approximately 2.0 or higher. The calculator outputs the **Sg** for each range as the projectile travels downrange so the user can see how the projectile’s stability changes as it travels downrange.

#### Selectable Outputs

**No Wind Trajectory:**

Self-explanatory and also excludes **Aerodynamic Jump** (below).

**Aerodynamic Jump** (Automatically accounted for in “Total Come Up”):

When firing in a crosswind, aerodynamic jump will result in a shift in the point of impact in the vertical plane caused by wind direction, wind speed, and reaction to gyroscopic stability factor. (Please see technical document.) This is in addition to the movement of impact due to the wind speed and direction itself and the shift in impact due to angular motion of the projectile downrange in both the vertical and horizontal plane.

The higher magnitudes of angular motion due to wind will cause increases in drag, resulting in increased time of flight. The increased time of flight will result in more drop and horizontal wind deflection.

In general, if aerodynamic jump, wind effects, and angular motion are not accounted for, misses are likely. The vertical shift in point of impact due to aerodynamic jump, increased drag effects due to angular motion of the projectile, and wind effects are accounted for in 4DOF trajectory solutions.

**Wind Drift** (Automatically accounted for in “Total Windage”):

Lateral trajectory deviation of a bullet from the centerline of the bore due to crosswind condition.

**Spin Drift** (Automatically accounted for in “Total Windage”):

This is a separate column that calculates the drift of the bullet, to the right for a right-hand twist and vice versa, due to the projectile’s aerodynamic and gyroscopic properties coupled with the fall of the projectile as it flies downrange.

**The value of ****Spin Drift** needs to be added to or subtracted from the **Wind Drift** of the projectile depending on the direction of **Wind Drift** and **Spin Drift**.

A positive number for **Spin Drift** is to the right, a negative number is to the left. You must know which way your projectile is drifting due to the wind and add or subtract the **Spin Drift** to obtain an accurate wind hold. For example: If the wind is from right to left (90 degrees) the projectile will drift to the left, say 3.25 MOA.

If the **Spin Drift** is positive, it is to the right, say .5 MOA. In this example you would subtract the .5 MOA of **Spin Drift** from the **Wind Drift** to arrive at a correct wind hold of 3.25 -.5 = 2.75 MOA of drift to the left. However, if the wind had been from left to right (270 degrees), the bullet would drift 3.25 MOA to the right and in this case, the **Spin Drift** would add to the wind hold. 3.25 + .5 = 3.75 MOA.

**Velocity:**

Calculated velocity at interval distances specified in either **STANDARD** or **METRIC** based upon input choice (Feet per second [Fps] or Meters per second [Mps]).

**Energy:**

Calculated remaining energy in either **STANDARD** or **METRIC** based upon input choice (Foot Pounds [Ft-lb] or Joules).

**TOF:**

Time Of Flight given in seconds from the muzzle to the distance specified.

**Reset To Defaults:**

Returns the calculator to the initial default settings.

**Calculate:**

Calculates **Total Come-Ups**, **Total Windage**, **Gyroscopic Stability** and all other user-selected Outputs.

**Total Come Up** and **Total Wind Drift** accounts for all the other outputs and provides a simple shooting solution. The selectable outputs are provided for shooters who wish to compare and contrast different input variables.

## More from Hornady®

For a more detailed discussion of the topics mentioned above and helpful tips on using the calculator, please refer to the Hornady® 4DOF^{®} Ballistic Calculator Technical Document. You will also find useful information on our FAQ page. We hope you find this calculator innovative and useful. We welcome any suggestions and input.

Back to the 4DOF CalculatorLearn about the 4DOF App

#### Additional Resources

- Degrees of Freedom | https://en.wikipedia.org/wiki/Degrees_of_freedom
- Drag Coefficient | https://en.wikipedia.org/wiki/Drag_coefficient
- Ballistic Coefficient | https://en.wikipedia.org/wiki/Ballistic_coefficient
- Gyroscopic Stability (Gyroscope) | https://en.wikipedia.org/wiki/Gyroscope
- Magnus Effect | https://en.wikipedia.org/wiki/Magnus_effect