Ballistic Data
The last key piece of "equipment" required is not an object, it is DATA. Ballistic data is key to
making long-range hits. This can be generated by one of the ballistic calculator computer programs
such as Sierra Infinity, Exbal, or JBM, or the shooter can get a set of data for his cartridge (or a
reasonably similar cartridge) and shoot on a known-distance range at intervals to generate data for
his rifle. External ballistics has been a studied for over a hundred years and the programs we
have today to predict the trajectory are pretty much "right on", provided that the input data
plugged in is good. With a solid 100-yard zero and a data-sheet from the computer, numerous
shooters have made first-round hits at 500, 700, and 1000 yards, at least,
The key inputs are: bullet ballistic coefficient (BC), muzzle velocity (MV), sight center over bore center distance, zero distance (100 yards recommended), and environmental conditions (station pressure and/or altitude, temperature and humidity).
I print out data cards to 1000 yards, fold them in half to make use of all the card space, laminate
them, and tie them to my scope mount.For example, my .308 load changes approximately 1 click (0.1 mil) at 1000 yards every 500' density altitude change (density altitude is a combination of station pressure and temperature rolled into one number). Knowing this rule of thumb, I don't need a sheet for every single change in altitude or temperature-- I can use the sheet I have and apply the rule. But if I am travelling to a much higher or lower location, I will print out a new card for that location. The article OPTICS FOR PRACTICAL LONG-RANGE RIFLE SHOOTING has an overview of rifle trajectory and what a data-card looks like. I normally use a short piece of shoestring or para-cord to tie the "current" data-card to the scope body. This prevents it from getting lost or blowing away, and is right where I can reach to look at it while on the gun.
You can skip to PRACTICAL LONG RANGE RIFLE SHOOTING - PART II: OPTICS or finish up this section with sample data cards.
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