adjusting the stock Benji open sights for windage

July 22 2009 at 5:25 PM

by Steve in NC  (Login q1q)

How do you adjust the stock Benji open sights for windage? I got an email yesterday...
July 20 2009 at 9:55 AM

...asking this question. It reminded me that, although the C9/392/397 manual tells how to adjust for elevation, there's no mention of windage. So here's the scoop.

1. At the front end of the rear sight are two slotted, #6-32 screws.
2. To move the point of impact to the right, loosen the left screw and tighten the right - thus moving the top half of the sight to the right.
3. To move the POI to the left, loosen the right screw and tighten the left.

Which leaves only the question: How far to loosen and tighten?

The sight radius of the Benji is 14", while one turn of the 32tpi screws moves the sight 1/32".
So each turn of the pair of screws moves the POI by 1/(14 x 32) = 2.23 milliradians = 7.7 MOA.

To convert that constant into simple arithmetic, suppose X inches is how far the POI needs to be moved, and Y yards is the range to the target.

Then the number of turns needed = 12.5 * X / Y

Notice that this gives a very nice and simple relationship, if the range to the target is chosen to be 12.5yds: Then each turn of the screws moves the POI exactly 1"

Examples: Suppose the POI is 2 inches to the left of the bull at 12.5 yards. 12.5 * 2 / 12.5 = 2. Loosen the left screw 2 turns and tighten the right.

Of course the basic math works with any range. It's just that 12.5yds makes it extra easy.

Suppose the POI is 1 inch to the right of the bull at 10 yards. 12.5 * 1 / 10 = 1.25. Loosen the right screw 1 and 1/4 turns and tighten the left.

And so forth.

Steve

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