Ballistic Calculator and Inputs

Ballistic calculators are extremely important to long range shooting. It makes an easy shortcut to determine your dope. However, I have seen, all too often, people rely solely on their ballistic calculators without understanding how they work. In previous blogs, I went over the formulas for determining distance and wind. I believe it is imperative to know these calculations. That way, if your ballistic calculator dies, you can easily make hits out to 500 or 600 yd. Possibly the biggest negative to a ballistic calculator is that they are only as good as the information that you put into them. Ballistic calculators are a very good tool to make shots at long ranges. But I would like for you to understand every aspect first, and how it effects the bullet, before moving on to a ballistic calculator. You should understand how barometric pressure changes your bullet impact. Also, look at the difference between two shots; one being only 10 fps faster or slower at a 1000 yds, and how dramatic the point of impact will be. Lets say you type the data into your ballistic calculator for 1000 yards, get down behind the rifle, pulled the trigger and you miss; well what went wrong? The ballistic calculator said to dial this many Mils. Now what? This is the reason you want to understand the aspects and the math behind it; so that you know that the answer your ballistic calculator gives you could potentially be incorrect and why. Most likely it's correct, but the information you entered is not. Let's go over ballistic calculators and the inputs that you need to know. Rifle and bullet information Barrel twist rate Bullet diameter Bullet speed Bullet length Bullet weight Ballistic coefficient Environmental Barometric pressure Ambient air temperature powder temperature Humidity Latitude and longitude Direction of fire Angle a fire Wind Before we jump into ballistic calculator, let's very briefly talk about the what, why, and how of each one of these aspects that we will be calculating. Barrel twist rate - In the ballistic calculator, this will give you a Gyroscopic Stability Factor number. This number lets you know if your bullet will be stable, or if it's over or under stabilized. Bullet Diameter - This is the caliber of the projectile in thousandths of an inch. Bullet Speed - This is extremely important to get accurate. This will essentially determine the majority of your bullet's drop. Bullet Length - Bullet length in inches. This will also effect the Gyroscopic Stability Factor number. A longer bullet will typically need a faster twist rate, and will have a higher ballistic coefficient. Bullet Weight - A heavier bullet is typically longer, which will impact the Gyroscopic Stability Factor number, and will normally have a higher ballistic coefficient. Ballistic Coefficient - This number is typically in G1 or G7. It lets us know how well the bullet flies through the air. For longrange shooting, a high ballistic coefficient is favorable. Barometric Pressure - Barometric pressure is the measurement of air pressure in the atmosphere; specifically the measurement of the weight exerted by air molecules. I look at it as the air being thinner as you climb in elevation, translating to the bullet being able to fly further, and the opposite as you decline. Ambient Air Temperature - Refers to the current air temperature. Powder Temperature - The current powder temperature or ammo temperature. Ideally we want our ammo temperature to match our ambient air temperature. Ammo temperature can differ greatly from the ambient air temperature, due to being in a hot car or in direct sunlight. Measure this with a laser themometer. Humidity - How much moisture is in the air (or air density). I really only take this into consideration when shooting past 1200 yds. I won't get into the science now, but the more moisture in the air, the thinner it becomes. High humidity = less air density = less resistance = less drop = high impact. Latitude and Longitude - This is where you are on planet earth, which helps determine coriolis. Latitude, I believe is, specifically for horizontal coriolis, regardless or longitude or heading. (Eg: northern hemisphere (right) or southern hemisphere (left)). Longitude or heading will determine vertical coriolis and the Eotvos effect. Direction of Fire - Compass heading or longitude. Different ballistic calculators may use a different name for the same input. Angle of Fire - Vertical angle, up or down hill will have the same effect. A cosine will be used. Wind - Wind speed and direction. That's a lot, and thats not even all of it. However, this should be more than enough to familiarize yourselves with the inputs of a ballistic calculator. I definitely recommend familiarizing yourself with each one of these aspects, how they affect the bullet, and how much. The best way I found to do this is enter the inputs separately into your ballistic calculator and see how much they actually change the bullet's impact. To get very detailed information about each one of these aspects, I recommend checking out the Sniper 101 series by Tiborasaurusrex on YouTube. As far as ballistic calculators go, I like free. JBM ballistics and ballistic XLR are my goto. Ballistic XLR is my personal favorite, because you can actually print these out and use them as a main ballistic table. I also use Strelok Pro, which is a phone app that works very well. Just keep in mind, batteries die, and when they do, you still want to be able to shoot. This is where ballistic XLR, to me, really shines. I print these out and have them laminated. Another really good option for a ballistic calculator are the Kestrels. I use the Kestrel 2700 mostly as a weather meter. It does come with ballistic hardware but being that it is a lower model, it's only good out to 875 yd. But, I will also use this as a backup to my backup, if I need to. I have found ballistic calculators with 5 inputs and some with15 or 20. Theoretically, the more inputs you have on your ballistic calculator, the more accurate the output. However, this also gives you more of an opportunity to get something wrong. Keep in mind ballistic calculators are only as good as the information you put in. I use a ballistic calculator, essentially, to confirm my dope charts. Or, if I'm shooting at an extreme range and I don't have a drop chart or data, then I will use a ballistic calculator. Most of the time, unless there's an extreme change in my environmentals, I use the dope card that is taped to the side of my scope. For me, probably the most valuable piece of equipment (aside from the rifle, scope and ammo) is the dope card that is taped on my rifle. The main information to focus on will be bullet speed, distance, and wind. You're not going to miss the target because you didn't calculate for the spin of the earth. And if you do, you're probably reading the wrong blog. So don't focus on things like coriolis and eotvos if you don't have your fundamentals down. Very rarely do I actually consider that into an equation, because the wind will have a larger effect. Go online and start playing with one of the free ballistic calculators. The links are on my website. The Overwatch