Dope cards and drop tables – How to generate and read them.
What are dope cards and how do I read them? Don’t worry, the thought police monitoring your office computer aren’t going to flag you for researching D.O.P.E. In the world of long-range precision rifles, the term D.O.P.E. refers to Data on Previous Engagement. DOPE is simply a collection of ballistic information comprised of critical factors that influence your bullets trajectory. Cataloguing and referencing this data gives a long-range shooter the ability to predict with great accuracy the point of impact of his or her bullet at a given distance, in a given atmospheric condition. Hitting targets at distance requires a more sophisticated approach than just ‘holding a little high ‘cause it looks kinda far’. If you want to consistently, and accurately, make shots at 600 yards and beyond you will need more than just a steady trigger finger and natural instinct. Making predictable and consistent long-range shots requires carefully calculated ballistic trajectory plots. The best way to achieve this is with “drop tables” that are calibrated against reliable DOPE.
Generating effective ballistic drop tables requires gathering and recording relevant information every time you shoot. Commercially available ‘modular data books’ are a good way to manage the DOPE you’ll be collecting. So called “modular data books” allow the shooter to customize their book by adding/removing pages and selecting different styles of charts and tables suited to his or her preference. Some websites even offer downloadable files that can be edited and altered by the user and printed at home. A quick internet search for data books will yield a vast array of options. However, a commercial data book isn’t required to log good data. Simply starting with a basic notebook and tracking relevant info like, elevation, temperature, range, how much elevation or holdover was used, impacts, misses, corrections, etc…is all you need to get started.
The first critical DOPE that you will need to develop a drop table is an accurate “zero”. Knowing your rifles “zero” means you understand precisely where your rifle’s point of impact is at a specific distance. The best place to find your zero is at the range where you can minimize as many variables as possible by shooting targets of a known size, at known distances, and in calm conditions. If you’re dedicated to developing pinpoint accurate data, then there’s no point in wasting your time with guesswork. Going out and shooting a paper plate hung from a fence post that you think is ‘round about a hundred paces away while resting on the hood of the truck isn’t the most productive approach. The objective is to get a 5-10 shot group inside a 1” circle. For most people this is done at 100 yards. Shooting from a bipod, off a bench or prone should give you enough stability. The more shots you can consistently place in that small area the better. Continue to adjust your scope’s elevation and windage until all your shots are landing within that 1” circle. Any deviations outside that 1” target will skew and distort your data at greater distances.
Next, you are going to measure your rifle’s muzzle velocity with an accurate chronograph. A chronograph will measure the speed of the bullet as it exits the muzzle. If you don’t own a chronograph then try to borrow one from a friend. Knowing your rifle’s muzzle velocity is critical when computing trajectories. Field verified chrono readings that you have recorded yourself will provide the best result. If you don’t have access to a chrono and you’re shooting factory ammo then use the velocity published on the box or from the mfg’s website. When measuring velocities with the chrono, make sure to get at least a 10-shot average.
Now that you have a rock solid, 100-yard zero, along with an accurate muzzle velocity, it’s time to start entering that data into a ballistic computer. Phone based applications like Desert Tech’s TRASOL app offer the most flexibility and convenience in the field but there are also PC based options if you are so inclined. Personal preference will likely dictate what’s best for you. Once you have decided on a ballistic computer it’s time to start programming. Most ballistic calculators will at minimum ask for the following information:
examples of available zero, bullet, and atmospheric data fields in the Desert Tech Trasol ballistic calculator
Muzzle velocity was taken care of at the range with the chrono. Hopefully you logged this into the DOPE record and have it at your fingertips. If not, start at the top of this page and try again.
Zero Range is the distance at which the gun was zeroed – typically 100 yards.
Bullet type, diameter, weight, and length are self-explanatory and can easily be found by looking at the ammo box or on the manufacturer’s website.
Ballistic Coefficient or BC is basically a number that represents a combination of the bullet’s drag coefficient and sectional density. In layman’s terms it refers to how easily the bullet flies through the air. BC is expressed in decimal format from 0.01 at the bottom of the scale, up to 1.0 at the top. The higher the number, the lower the drag, the flatter the trajectory. A good place to start is with the manufacturer’s published BC number. As you advance in the process it might become necessary to adjust this number slightly. This is called trueing the data. More on this later.
Drag Models are mathematical calculations used to predict the effects of drag on a bullet in flight. There are several drag models that apply to small arms projectiles but in most cases the G1 model is recommended. Sometime manufacturers will indicate a preferred drag model for their bullet. It might be worth experimenting and finding which works best for you.
Height Over Bore or Sight Height is a measurement from the center of the bore to the center of the scope. This can be obtained by taking a single rough measurement with a ruler and eyeballing. Or, if you prefer a more precise approach then measure your bolt diameter, and scope tube diameter, and then divide that sum by 2. Then measure from the top of the bolt to the bottom of the scope tube and add the previous sum.
Atmospheric conditions have a big effect on ballistic performance and the ballistic computer like Trasol will ask for this. Using a weather meter to gather temperature, pressure, altitude, dew point, and wind velocity will yield the most precision. If you have a basic weather meter that only captures temperature and wind speed that’s ok, it’s better than nothing. And if you don’t have a weather meter then looking at your local weather data online or within an app can help fill in the blanks. The most useful atmospheric data point in most cases is the Density Altitude. DA is a single number that accurately represents multiple atmospheric values. Weather apps will often cite a density altitude, or you can use a DA calculator which will compute the value from a given altitude, temperature, barometric pressure, and dew point. A big part of gathering DOPE is recording the atmospheric conditions each time you shoot. Having reference material on hand that can tell you how differently your rifle performs in hot, humid, sea level conditions versus cold, dry, high altitude conditions is critical. This record of subtle performance variables, DOPE, will allow you to fine tune your drop tables and enable you to make first round hits at extended distances. The farther out your target the more heavily these factors weigh on your trajectory.
After you have programmed the ballistic computer with all the required data it will then be able to produce a table or ‘solution’. The table can be set to list bullet path or ‘drop’ in a variety of metrics including MILS, MOA, clicks, inches, etc…The drop values will be listed for each increment of distance to the target. In this example the path is listed in MOA and for the target distance of 1000 yards, the bullet drop is calculated as 26.4 MOA. This means the shooter would need to dial or hold 26.4 MOA of elevation in order to hit the target.
Now that you have accumulated enough data to program the ballistic computer and generated a drop table it’s time to work on calibrating the results against some real-world feedback. Trueing the data is a process of fine tuning the ballistic trajectory in the computer so that it matches what is occurring in the field. Modern ballistic computers can provide astonishingly accurate solutions out to 600 yards without too much trouble. But as you move out to 1,000 yards and beyond it sometimes becomes necessary to fine tune the calculation. For example, you might need to slightly adjust the BC by a tiny fraction so that your drop table matches your field results at extended distances. The amount of ballistic trueing you end up doing will vary. You might find that one rifle or caliber matches the calculated results perfectly at the distances you are shooting. Other times it might need a little finesse to align with the real-world results. Ultimately the quantity and frequency of data logged will come down to personal preference. Once you have a reliable drop table developed you might find that it’s no longer necessary to log every single shot for that particular rifle. Tracking field results in extreme circumstances might be all that is necessary as you move forward. For example, if your drop table becomes acceptably accurate after trueing the data you might only record data for high angle shooting and point of impact shifts during extreme weather conditions. Some ballistic apps even offer the option to log field data, similar to what can be done with data books. This minimalist approach might provide you with an opportunity to streamline your kit and become even more low-speed, high-drag.
Gathering DOPE and developing accurate trajectory tables can be a time consuming endeavor. It’s also a lot of fun. As you record detailed data over time, the repository of accumulated information will give you an almost uncanny ability to predict exactly where your bullet will impact, at great distances, in a variety of conditions. DOPE provides a heightened understanding of your rifle’s behavior and provides an extreme advantage in long range shooting activities. Sophisticated ballistic computers and apps are readily available and accessible even for the uninitiated and allow every sportsman the opportunity to shoot with a level of precision and confidence that was unfathomable in generations past. Whether you are entering the world of competitive long range rifle events or hoping to eliminate missed opportunities on game at increased distance, the benefits of DOPE are undeniable.