We approximate a minute of angle to be 1 inch at 100 yards.  The true figure is extremely close to that amount.

On MVA tang sights, the graduated scale has 20 graduations per inch, so each graduation is .05". Each graduation counts for 5 "MOA" when you use the vernier, but the term MOA is used loosely.  How much the POI changes with 1 "MOA" on the vernier scale depends on the sight radius, and works out to an inch at 100 yds for a sight radius of 1 yard or 36".

For sight radii of different lengths, the amount of POI movement in inches for .01" movement of the rear aperture would be equal to 36 divided by the sight radius in inches.  For example for a 24" sight radius, move the rear sight .01" (1 nominal "MOA" of the scale) and the POI will move 36/24" or 1.5 inches.

On my High Wall 32-40 with a 30" barrel, sight radius with my MVA tang sight is about 33 1/4" at a setting of 10 (changes with slider position on the staff - about 33 3/8" at 260).

And yes, how many "MOA"s of movement of the rear sight is needed between, say, 100 and 200 yards (or other change in target distance) is dependent on the load performance (bullet speed, BC, etc) and has to be determined by actually firing at those distances and comparing the sight settings.

Excellent point, CajunRebel.  Oversight on my part to point out that I was talking about the vertical or elevation scale.  On my MVA tang sight, the small windage graduations are .02" so 2 "MOA" each.  My windage sliders on the MVA sights with windage on the assembly with the eye cup do not have a Vernier scale, but simply a single line opposite the windage scale that has 20 graduations.

Two ways to figure yours. Calculation or prove it on paper.

Zero close for a small point of impact group, 25 yards. lot of shots then find center of impact with a framing square. Box in the holes then X through the corners for center. Don't count wild shots. Use the "normal group" only.

Then move the sight a lot. 10 graduations, shoot another group on the same target. Do the same thing box them in then X

Measure the distance between first and second groups center of impact, divide by 10 and you will find impact movement per graduation. Expand the 25 yards to 100 by multiplying x 4 and you have sight movement in per graduation.

In practice I do it by calculation or the Handy little Chart Lyman provides with sights. Then at the range prove the calculation by using the shoot and measure method. Only taking a few shots to confirm I calculated properly.  

I can scan the chart and send it to you if you like

Boats

Will scan it this afternoon and send it.

Boats

Chart is out to you via Email

Formula goes like this

Measure your sight radius then divide it by 3600 (number of inches in 100 yards). Measure your graduation spacing.  Multiply first result by the second.  Result is bullet movement one graduation at 100 yards.

Couple of ways to improve accuracy of result. One is measure 10 graduations & divide by 10 to get value of one.  And I prove on paper after calculation. Click sights I use a dial indicator to measure movement & value of a knob turn.  Indicates any backlash in the screw. Takes a good click sight to have minimal backlash.  Vernier sight much more accurate.

Boats

Boats, something doesn't seem quite right with that. For example with 30 inch spacing 30/3600=.00833. The graduation is going to be only a few thousandths so the movement at 100 is going to be impossibly small. Maybe divide the spacing result by graduation result instead of multiplying?

IOwnDoubles wrote on May 11^th, 2016 at 11:44pm:


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