As soon as I hear back from Dustin at Real Avid, I will show you how to adjust the sight by whatever amount you choose.
I contacted Dustin (left a voice mail, he was out of the office) to find out what the thread pitch is on the magnum drive screw as it is called on the Real Avid Master Sight Pusher.
Once we know that, we can calculate how many turns move the sight how far.
That screw is listed as extra fine thread in their documentation, but no mention of the thread pitch or the number of threads per inch (TPI) .
But, for giggles, lets say it is a 40 TPI thread , it looks to be at least that many threads per inch.
A 40 TPI screw has a pitch of 1 divided by the TPI, so in this example, 1 divided by 40 yields a pitch of 0.025 inches.
That means, that for a nut installed on a screw possessing 40 TPI, on full revolution of the nut, or the screw, will move the nut or the screw 0,025" in a linear direction.
So, how does knowing the TPI help us? Well, if we know how much we need to shift a sight from left to right or right to left to obtain the POA/POI relationship we desire (Point of Aim, Point of Impact) and we know the TPI of the screw, we can move the sight pretty darn close with only one or two tries of the slide in the sight pusher.
How do you calculate how far to move the sight? Read on if you dare!
Iron Sight Correction Formula
Remember the acronym F.O.R.S. Front (Sight) Opposite, Rear (Sight) Same.
You move the front sight the opposite of the way you want the bullet to move, and /or you move the rear sight the same way you want the bullet to shift.
Here's how to calculate how much to move a sight, or to add to it or subtract from its height. I'm going to use a M! Garand as an example, because the numbers will be bigger and easier to visualize, but this works for handguns too.
We'll say the distance to the target is 100 yards (3,600 inches) and the bullet is hitting 9 inches to the right of the bullseye, which was our aiming point,
A = The distance from the rear sight to the front sight measured in inches. For an M1 Garand, this is 27.875 inches if my memory is correct.
B = The distance from the barrel of the rifle to the target in inches. Example: 100 yards is 3600 inches , 200 yards is 7200 inches, 300 yards is 10,800 inches, etc.
C = The CHANGE in drift required in the front (or rear) sight to change the elevation, or the windage. We'll go with windage here. The amount (answer) will be in hundredths of an inch in most cases. Sometimes thousandths of an inch!
D = The height ABOVE or BELOW, or LEFT OR RIGHT of the bull's-eye of the target that the bullet is off by, again stated in inches. And assuming of course that the bull's eye was your point of aim. 9 inches in our example here.
Actual Relationship
A is to B, as C is to D. Therefore, the formula is as follows:
A C
---- = ----
B D
Restated: A x D = B x C or C = (A x D) / B
So if we plug in your numbers, we get:
C = (27.875 X 9) / 3600 OR C= 250.875 / 3600, therefore,
C= 0.0696 inches which is the amount that you need to drift the rear sight by, to the left .
So, if our sight pusher has a 40 TPI thread, and we were using it to drift that M1 Garand's rear sight to the left (Remember F.O.R.S. Front Site Opposite, Rear Site Same) to get that bullet on target at 100 yards so that POA and POI coincide.
So, if our site pusher has a TPI of 40, that's a pitch of 0.025, so we divide the amount of correction , above it's 0.0696 inches by 0.025", we find that we need to make 2.78 revolutions of our screw to move the sight that 0.0696 inches.
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