Drag Model - There are various models for ballistics drag. The G1 drag function is the industry standard, and virtually all printed data or documentation that is to be found references this drag model. However the G1 drag model is not particularly well suited to modern low drag bullets, so other options are provided for the serious long range shooters. If you are shooting at ranges under 800 yards the G1 drag function will most likely be adequate, and sometimes for particular bullets it will be an excellent model for the entire flight. However, if you find that the results for longer ranges are lacking a bit for a particular load (especially for boat-tail low drag bullets), you may want to investigate using some of the newer drag models such as the G5 or G8. There's not much printed data to be found for these other drag models, so you will have to do the experimentation yourself and carefully record real-life shooting observations, then run simulations using different drag models and drag coefficients until you find a combination that fits well. You can not use a G1 drag coefficient with any other drag model and expect an accurate result, so it takes a bit of experimentation to find the drag coefficient which suits your bullet for any other drag model, although the end result may be improved computational accuracy.

Why all these models? Because there is no known single equation that can be used to exactly describe the flight of a bullet. Many of the air drag parameters are only able to be described by assembling real-time observations taken on radar ranges into a piece-wise drag model. Most bullet manufacturers don't have mile long radar ranges to model ballistics on (including me!), so they use a regular range to see how their new bullet relates to the "standard" models that ballisticians have spent years developing. They will then publish a correction factor known as the ballistic coefficient which relates their bullet to the standard model. The G1 model is most often used since it is a good general purpose drag model for supersonic ballistics flight, and meets the needs of most shooters and hunters.

Ballistic coefficient - The coefficient of drag for your bullet, using a G1 drag function. This can be found in your bullet manufacturer's documentation. All published BC's are for the G1 drag function unless they explicitly state otherwise, and are generally a number between 0.300 - 1.000.

Projectile Weight - The weight of your bullet, in grains. This can usually be found on the bullet box or in the manufacturer's published data.

Initial Velocity - The muzzle velocity of your bullet / rifle combination. The best way to get this is with a chronograph, but you can also estimate it from known combinations. For example, a 168gr SMK generally shoots about 2650 ft/s out of a 26" barrel in most match grade loads. This is acceptable, but for the best accuracy consider borrowing or buying a chronograph.

Zero Range - The range at which your rifle is set to "zero". If you zero your rifle on a 50 yard range, this would be 50 yards. A popular zero for many hunting rifles is 200 yards, which seems to be a good compromise between bullet path and maximum point blank range.

Sight Height - The height of the sighting system of your rifle above the bore of the rifle. For scopes this is usually between 1.5-1.8, but the bigger your scope and the taller your scope rings, the larger this will be. An easy way to measure is to measure from the bottom of your scope objective bell to the top of your rifle barrel, then add this number + the objective bell's radius + the barrel's radius (at the point you measured), to get a very close approximation.

Angle to Target - If you are shooting up-hill or down-hill at your target there can be a big change in the bullet trajectory. For up-hill angles use positive angles and for down-hill use negative. Example: If your favorite hunting location is from the top of a hill looking into a valley, you might shoot at a down-hill angle of 30 degrees. For this scenario you should use the value -30 here to generate an accurate ballistics table.

Wind Velocity - The wind speed in miles per hour. There are several good ways of estimating wind speed, but the best is to measure it with an anemometer.

Wind Angle - If you wish to generate a windage table you need to enter the angle from which the wind is blowing. In this simulator, a direct headwind is 0 degrees, a wind from right to left is 90 degrees, a tail wind is 180 degrees, and a wind from left to right is 270 degrees (or -90 degrees).

Max Range - The maximum range you need data for. The engine will give up whenever the bullet is dropping faster than it is progressing forwards, so you can't get data at extreme long ranges for most cartridges. But this will cover all possible shots that you might actually be able to make, for any cartridge up to small artillery.

Step Size - My hosting company gets a little upset when this script uses up all the resources, since ballistics calculations can be quite intensive. To speed things up a bit I have added this step size. The solution is just as accurate, but the solution won't store data for every yard. If you enter a step size of 10, you will get data for every 10 yards, which uses up only 1/10th the memory of a standard solution with no loss of accuracy.