Ballistic Calculators: A Quick Guide

Ballistic Calculators: A Quick Guide

What is a Ballistic Calculator?

A ballistic calculator is exactly what it sounds like. It is a calculator that uses the ballistic profile of your rifle to generate a data sheet detailing your required elevation adjustment and wind drift at specified distances. It will use the information you provide it to calculate this information.

How to use a Ballistic Calculator.

Using a ballistic calculator is fairly simple; all you are going to do is enter information into a webpage or app, and it will generate the sheet for you.

What will it ask for?

It will ask for:

- Starting Distance.

- Maximum Distance (The furthest distance you want data for)

- Intervals (How many different holdover calculations you want in whatever intervals you want to the maximum distance)

- Ballistic Coefficient

- Drag profile (G1 or G7)

- Velocity of your projectile

- Barrel Twist (eg, 1:10" twist)

- Bore diameter

- Bullet weight in grains

- The range the rifle is zeroed at.

- Sight Height

- Shooting angle (Are you shooting up or down a hill)

- Wind speed

- Wind angle

- Altitude

- Air pressure (29.92 at sea level)

- Temperature

- Humidity

 

How do I collect this data?

To find out how to collect this data, please see our Blog, which explains how to do this. Click HERE.

How to enter it into the calculator?

Once we have collected our data, the next step is to enter the information into the calculator. For this example, I will be using the free ballistic calculator from Hornady to test.

For this test, I will be doing a 6.5mm Creedmoor that I have tested previously with factory ammo, assuming flat terrain and 10mph right-to-left wind.

Another calculator you can use is the "applied ballistics" calculator, which is an industry leader and pairs with common brands which produce binoculars, kestrels, chronographs and even watches to aid in long-range shooting.

Something to check.

Filling out the information is quick and easy; it's just filling in the boxes, and this can be done just about anywhere. The only consideration you need to have is making sure the units of measurement you are entering match what you collected.

For example, was your Chronograph measuring Metres per second, and the Calculator is asking for Feet per second?

You will notice down the bottom that some features are unclicked. The main ones which could be very useful to click apart from distance, total come up (Elevation adjustment), and total windage (windage adjustment) are energy and velocity. These just tell you how much energy the projectile has left at certain ranges and how much velocity is left. This is helpful for finding out how far you could ethically hunt an animal and how close the projectile is to becoming transonic.

Explanation of measurements possible.

I unclicked wind drift and spin drift, as these two are pre-calculated by the "total windage" bar. Spin drift is a phenomenon in long-range shooting where a bullet's spin causes it to drift slightly horizontally over long distances. This drift is in the same direction as the barrel's twist (Generally, rifles have a right-hand twist). In shorter ranges, it's usually negligible, but at longer distances it can become significant. In this particular calculation, the spin drift is 19cm at 1000m. Most calculators will automatically calculate this and present the actual hold required in the "total windage" bar. You can choose to do the math if you want, but it is easier to let the calculator do it.

For example, the wind drift for this rifle at 1000m with a 10mph right to left wind was 2.23MRAD to the and the spin drift was 0.19MRAD to the right. You would subtract the spin drift from the wind drift in this instance because if you dial 2.04MRAD, the spin drift will account for the remaining 0.19MRAD. This gives us 2.04MRAD of total required adjustment. This is the measurement given by "total windage".

If the wind was blowing the other direction, you would add the spin drift to the wind drift, 2.23MRAD + 0.19 MRAD = 2.42MRAD. The reason for this is that if you are adjusting right, the (right-hand) spin drift will reduce the amount of adjustment required in the turret, whereas adjusting left will require you to adjust more to counteract the spin drift to the right.

- Aerodynamic Jump is a small vertical deflection of a bullet due to the initial precession cycles as it weathers into the wind. (This is usually negligible)

- TOF means time of flight, which just gives you the time the projectile takes to reach certain distances.

- Gyro means gyroscopic stability. This is basically a measure of how stable the projectile is. Hornady states that a minimum Gyro rating of 1 is required to be stable in flight. Another thing worth noting is that the projectile will become rapidly more stable as it flies downrange. This is because the projectile's velocity is slowing at a faster rate than its spin. This particular test has a gyro of 1.73 at 100m and at 1000m, a rating of 4.09.

- No wind trajectory means the trajectory the projectile would take if there were no wind effect on it.

Now I would be remiss if I didn't at least mention the Coriolis effect. We get it, you played Call of Duty Modern Warfare. The Coriolis effect affects the flight of a bullet in the Northern Hemisphere so that when firing north or south, the bullet sways to the right and in the Southern Hemisphere, to the left. The more your firing line is in the east-west direction, the less the effect of the Coriolis. Firing east and west can result in the projectile hitting further or shorter than the target as the Earth spins under it. This effect is caused by the Earth rotating under the bullet's trajectory. The LAPUA website does a really good job of explaining this in great detail. However, being that it is only a very small effect and really only at distances past 1000m. It's not as much of an issue as people think it is. With a 1000yd shot shooting directly north in California, the deflection is only 2.8inches or 7.1cm.

What does a data sheet look like?

The data will list whatever you pre-selected in our previous image.

This is indicative of what most calculators will present. If you change the information entered, it will change the information presented. So if I want to make a shot at 800m, I will need to dial up 6.78MRAD and adjust right 1.47MRAD. Being that MRAD comes in a 0.1MRAD adjustment, you would round to 6.8MRAD and 1.5MRAD.

This can be a fairly involved topic and a little abstract to some people, but the team at Optics Warehouse can point you in the right direction to get all the tools to help with this.