For guns with iron sights, you can make a few simple measurements and calculate how much each step on the ramp changes the sight adjustment. To get an accurate value, make careful measurements and record them in inches. First you need to measure how far the rear sight can move up and down. To do this, put the rear sight on the lowest step of its ramp, and measure the distance from the top of the barrel to the top of the sight's blade. Now put the rear sight on the highest step of its ramp, and again measure the distance from the top of the barrel to the top of the sight's blade. Subtract the first distance from the second to get the vertical movement of the rear sight. Divide the vertical movement by the number of steps in the ramp. This gives you the vertical movement per step. The same procedure is used for sights with a screw adjustment. Turn the screw in until the rear sight is in its lowest position, and measure its height above the barrel. Next, turn the screw out 10 clicks (or increments) and measure the sight's height again. Now subtract the first distance from the second to get the vertical movement of the rear sight. Divide the vertical movement by 10 to get the vertical movement per click. To get the sight base, measure the distance from the rear sight's blade to the highest point of the front sight. Finally, divide the number 3,438 by the sight base distance (in inches), and then multiply that number by the vertical movement per step. The result is how many MOA (minutes-of-angle) each step of the ramp changes the sight adjustment. For example, on a particular gun, the rear sight's distance above the barrel in the lowest step of the ramp is 25/64 of an inch, while its distance above the barrel in the highest step is 33/64 of an inch. Subtracting 25/64 from 33/64 results in a value of 8/64. Any fraction can be converted into a decimal number by dividing its numerator (top number) by its denominator (bottom number); thus, the rear sight's vertical movement is 0.125 inch (8 divided by 64). The ramp on this particular gun has 10 steps, so the vertical movement per step is 0.0125 inch (0.125 divided by 10). Next, the distance from the rear sight's blade to the highest point of the front sight is 19.2 inches. The number 3,438 divided by 19.2 is 179.1. The number 179.1 multiplied by 0.0125 (vertical movement per step) is 2.24. Thus, each step of the ramp changes the sight adjustment by 2.24 MOA. |
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