| Bullet Drop, Wind Drift and Making Scope Adjustments To Compensate |
| By Brad Blaine |
| Hunting 101: An informative series for the beginner and expert hunter alike. |
| The following formulas will help you in determining how many clicks to adjust to get “on target” either while target shooting or hunting. First, you must calculate the bullet drop or wind drift. This is accomplished through the use of ballistics tables and wind drift charts. These can be generated by computer programs like Point Blank or Sierra Infinity pretty easily if you have input the load data (things like ballistic coefficient, chronographed velocity, etc.). These charts may even be supplied by the ammunition manufacturer if you’re shooting factory ammo. The best reference, however, is measuring your bullet impact at that range from your gun. There is no better indicator than actual shooting. However, if the ballistics tables honestly match what you’ve shot out of your rifle on the range, then you should be able to compensate from the tables with relative confidence. For example, I have a Remington 700 Sendero Stainless Fluted in 7 mm Remington Ultra Magnum (RUM). I handload for it and have chronographed my most accurate load (Sierra Match King 168 grains over top of 88.2 grains of H-1000) which is cruising just over 3000 FPS at the muzzle and my rifle is sighted in 3.25 inches at 100 yards. At 500 yards, my ballistics program says that it will be 23.83 inches low. Second, you must understand Minute-Of-Angle (M.O.A.) and be able to calculate it at the distance you’re shooting. Though the calculation is rather lengthy, the end result is that 1 M.O.A at 100 yards roughly equals 1 inch. At 200 yards, 1 M.O.A. equals 2 inches and so on. So roughly, Equation 1. Minute-Of- Angle Equation 1 M.O.A @ distance X = distance in hundreds of yards / 100 For example, 1 M.O.A. @ 500 yards = 500 / 100 = 5 inches Finally, once you’ve obtained the bullet change (drop or drift) and you know the M.O.A. value (in inches) at the distance you’re shooting, you must know how many clicks to make on your riflescope to compensate for the change in point of impact (P.O.I.). To do this, you simply fill in the following equation: Equation 2. Minute-Of-Angle Scope Adjustment Equation Bullet change in inches (drop or drift)/ 1 M.O.A. value @ distance X = M.O.A. scope adjustment |
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