Williams Receiver Sight Adjustment

armilite

November 10, 2009 16:23

I'm pretty sure they are a reference point only. Say if they were a 1/4 or 1/8 inch, there just would not be a whole lot of adjustment in the sight. It would take 4 marks to move it 1 inch at 100 yards or 8 marks to move it 1 inch if each line was an 1/8 inch. I haven't seen any in a while but my memory tells me there are not that many lines.

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RCrosby

November 11, 2009 02:51

Reference marks only, as far as I know. Even if specific values were assigned barrel length would dictate the popular "your mileage may vary". Shoot a few groups to establish a firm center point, move the sight up or down 4 lines, shoot for another center point yeilding group and work out the math for your rifle.

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beantownshootah

November 11, 2009 04:29

quote:Originally posted by travis3
Does anyone know how many inches each mark stands for on a Williams 5d Receiver Sight or are they there for a reference point only?

Reference only.

The only way that adjustment marks on a receiver sight can be exactly calibrated for minutes of angle (or if you prefer, inches at 100 yards) is if the manufacturer knows the exact distance between the front and rear sights (eg the sight radius).

While the marks ought to be calibrated for a certain "standard" sight radius, unless your gun happened to have the EXACT same sight radius, they wouldn't otherwise correlate.

If you knew how much distance the rear sight moved for each mark (or "click") and the sight radius of your particular gun you could mathematically calculate the minutes of angle change per click.

Alternatively, if you knew the "standard" sight radius that the sights were calibrated for (assuming they were, in fact calibrated at a certain radius) and the minutes of angle per "click" at that radius, and you knew YOUR sight radius, again, you could mathemetically calculate the minutes of angle per click for your particular gun.

Its *possible* that Williams could give you the information about how many mm (or fractions of an inch) each line moves the rear sight, or what sight radius these are supposed to be calibrated at, then you could take it from there.

In practice, your best bet to figure out what the marks mean is some real world testing.

I think Rcrosby has this right.

If you need to know exactly, try zeroing your gun using some 1" grid paper at 100 yards. Shoot a group, adjust the sights by a specific number of clicks to get to zero, and then using the 1" grid you'll be able to exactly see how many clicks equal 1".

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RCrosby

November 11, 2009 13:28

O.K.
I had a little time to play with the math. Not as good as time on the range, but may be instructive.
The old Foolproof sight on my .257 has 20 hash (sp?) marks spanning 1/2", or about .025" between them.
The distance from the rear sight to front is 27" and the distance to targets on a 100 yard range is 3,600 inches. (Hope I've got that right.) That gives us a ratio of about 1 to 133.33.
So,
each mark SHOULD, on my rifle, equal about 3 1/2 inches of elevation. Some day I'll figure out how many clicks it takes to span that .025 inches.

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travis3

November 11, 2009 13:54

Want to thank everyone for thier help. I think I have it now. On my Marlin 38-55 CB it seemed to work out to be close to 4 inches at 100 yards. Thanks again.

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beantownshootah

November 12, 2009 07:57

quote:Originally posted by RCrosby
O.K.
I had a little time to play with the math. Not as good as time on the range, but may be instructive.
The old Foolproof sight on my .257 has 20 hash (sp?) marks spanning 1/2", or about .025" between them.
The distance from the rear sight to front is 27" and the distance to targets on a 100 yard range is 3,600 inches. (Hope I've got that right.) That gives us a ratio of about 1 to 133.33.
So,
each mark SHOULD, on my rifle, equal about 3 1/2 inches of elevation. Some day I'll figure out how many clicks it takes to span that .025 inches.

Here's a double check, for pure mathematical "coolness".

Bet you thought you'd never need trigonometry again! WRONG! [;)]

Imagine a triangle:

-One point is your front sight.
-One point is your rear sight BEFORE you move it.
-The last point is your rear sight AFTER you move it over one hash mark, or 0.025".

Note that this is a right triangle, since the movement of the rear sight is exactly perpendicular to the line drawn between the front and rear sights.

So now all we need to do is calculate the itsy-bitsy angle at the front sight to know what the effect of moving the rear sight is.

By simple trigonometry, in a right triangle, the tangent of an angle equals the opposite (in this case 0.025") over the adjacent (in this case 27").

So the tangent here is (0.025"/27") or 0.00092592

Using a scientific calculator, the ANTI-tangent for that value is 0.053016 degrees.

Remember, that a "minute of angle" just refers to 1/60th of a degree. So you can just multiply the number of degrees by 60 to get the minutes of angle.

In this case (0.053016 x 60) = 3.18 minutes of angle.

That's your answer.

People say a minute of angle equals one inch at 100 yards, but its not exactly true. That's just a quick approximation that is "good enough" for most practical shooting. If you want to be absolutely mathematically precise, one minute of angle technically subtends 1.047197" at 100 yards. So if you multiply your 3.18 minutes of angle by 1.047197, you get 3.33"

That's how much your point of impact should move if you start with a sight radius of 27" move the rear sight over 0.025"

To generalize this formula to ANY rear sight the movement of point of impact in inches at 100 yards will equal:

(62.5182) x (anti-tangent in degrees of [distance of rear sight movement/sight radius]).

That's it.

If you prefer to use true minutes of angle, you can just use 60 instead of 62.5182, etc.

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Williams Receiver Sight Adjustment

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