Sighting-In My New Scope

Posted on January 03, 2008 by Stephen

I went out the LPRG today to sight in my new scope. The scope is a Bushnell Banner Dusk & Dawn 6-24X40 Riflescope. This scope has DDB multicoated lenses to maximize transmission of light for excellent low-light and full-light clarity. A fast-focus eyepiece and wide-angle field of view combine to allow focusing-on and follow moving game easily. My scope has the Mil-Dot reticle with 1/4-MOA fingertip-adjustable windage and elevation knobs with resettable dials. There's an easy-grip power change ring for fast, convenient zoom changes. These scopes are fully waterproof, fogproof and shockproof.
I started out by shooting at a 25yrd target. The first shot was 3.5 inches low but the windage was right. I cranked up the elevation and walked the shot pattern up into the 10 ring. I put three more rounds into the 10 ring before moving to the 100 yrd target.

At 100 yards the first three shots were ~1.25 inches low, ~1.5 inches left. There was a tail wind and gusts coming from both sides (left and right). I cranked up the elevation first. Using the Mil-Dot reticle, I was able to make the first adjustment to within ~0.25 inches low of center (three shot group). I left the elevation there and worked on adjusting the windage. Again I used the Mil-Dot to guess at the correct windage but I over corrected and sent the next three shots ~1.25 inches right of center. A second windage adjustment put the next three within ~0.25 inches right of center. I worked the windage two more times as best as I could with the gusts coming from left and right. After 15 shots I was close to center and I sent the next 20 shots into the red with and average 2 MOA for all 20 shots.

I will have to do this again when I get some taller rings. The rings I was using today had a very small clearance for the X40 (about 2mm) which is not enough space for the lens covers. Oh darn, I guess I'll have to go shoot some more.

Here is some information on the Mil-Dot reticle.

The "Mil" in "Mil-Dot" does not stand for "Military"; it stands for "milliradian." The radian is a unitless measure which is equivalent, in use, to degrees.

One milliradian = 1/1000 (.001) radians. So, type .001 into your calculator and hit the "tangent" button. Then multiply this by "distance to the target." Finally, multiply this by 36 to get inches subtended at the given distance.

With the calculator in "radian" mode, type:


So, one milliradian is just over 3.6 inches at 100 yards. If we extrapolate, two milliradians equal about 6 feet at one-thousand yards. You'll see the importance of this, shortly.

The mil-dot can also be used to estimate distance to target. If we have a known target that is 6' tall (2 yards tall) and the top of the target is on the +2 mil-dot and the bottom is at the -2 mil-dot we can calculate the distance by taking the known height of the target in yards and divide by the number of mil-dots times 1000:



To work with inches we need to change the equation above slightly. If my target is 2 inches tall (the center of 10 ring) and it covers 0.5 mil-dot in the reticle we use this equation:





For my scope, this works at the 12X power only. For other powers I need to multiply 36 inches by the power of 12 (i.e.; 6X = 36*2 = 72 inches, 24X = 36/2 = 18 inches. This is why I over estimated the windage at 100 yards on my first group of three.
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