Mathemetician needed

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cheygriz

cheygriz

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Does anyone remember the formula for rear sight movement??

I have a 1911, 4 inch barrel, fixed sights, that shoots 3 inches to the right at 10 yards.

How many thousandths will I need to drift the rear sight to bring it on target??

Thanks in advance,
Griz.
 
Many years back I worked as a surveyor. Your math problem is one of triangulation. Had you asked me to work this problem 40 years ago I would have said sure.

Today I say : trial and error. Controlling drift adjustment accurately to the 1/1000 is a stretch anyway. If your measurement of sight to target is off by a few fractions of an inch or distance between front and rear sights is off by a few 1000's the whole equation is skewed .

Trial and error.
 
It's a problem with similar triangles. You can write X/4 = 3/360 where X is the distance to move your sight. I get .033".

Your sight radius probably isn't exactly 4", so you should substitute that where I put the 4.
 
3/360 = 0.008333

so 8 thousandths

Edited:

I forgot about the 4" sight radius so multiply by 4

33 thousandths.

It's like a lever.
 
Last edited:
Waveski said:
oday I say : trial and error. Controlling drift adjustment accurately to the 1/1000 is a stretch anyway. If your measurement of sight to target is off by a few fractions of an inch or distance between front and rear sights is off by a few 1000's the whole equation is skewed .

Trial and error.
Click to expand...
That's how I do it.
 
Barrel length and sight radius are different. Barrel length is the length of the barrel. Sight radius is the distance from the back of the rear sight to the back of the front sight.

The sight radius on an autopistol with a 4" barrel is going to be something like 6".

In a pistol with a sight radius of 6" that is shooting 3" to the right at 10 yards, drift the rear sight 0.05" (1.27mm) to the left to correct the point of impact to the point of aim.
 
I'm no mathematician, but I am a gunatician!

Go to the range. Bring a brass punch pin (or drive pin) and a small brass mallet. Make a mark on the slide to tell you where the sight is set now. Tap the rear gently in the direction you want the bullet to move. Assumin it's a fixed sight, of course. Check that it moved, if not, tap it harder or use a heavier mallet. Moved a bit now shoot 5 rounds. If not where you want it, tap some more.

If still no good aim three inches in the other direction, blame the ammo and call it a day.
 
Last edited:
I find it amusing that some folks put that much concern into their pistols.

Wanting pistols to be as accurate as rifles with high dollar scopes.

But, to each their own...
 
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Take the Ratio of (rear sight to front sight)/(front sight to target). You'll find that it's ~0.0166, but since you haven't specified your sight radius I assumed 6".

Any adjustment of POI requires moving the rear sight by the Adjustment x Ratio.
 
:)Thanks, guys. I appreciate your time and effort.

John, I forgot about the difference between barrel length and sight radius. Thanks for the reminder.
I just ordered a "sight pusher" adjustment tool from Brownell.

I'll mark off .004 with the micrometer and go from there.

I realize that trial and error is the normal procedure, but I always look for a more precise, "one adjustment" solution when possible. I guess I'm just persnickety!:D
 
“
Correcting Sight Height
If your rifle or pistol is shooting high or low, there is a formula you can use to determine what the correct height for your sight should be.

Terms
Amount of Error: Measure in inches the distance from the bullseye to your shot.
Sight Radius: Distance in inches from the front sight to the rear sight. *
Distance to Target: The distance in inches from your shooting position to the target.

Note: Be sure that your rear sight is at its mid-point before you shoot.

Formula

Amount of Error X Sight Radius
= Sight Correction Needed
Distance to Target
If you are shooting low, you would replace your front sight with a lower sight, and conversely, if you were shooting high, then you would replace your front sight with a higher sight. Add or subtract the number of thousandths needed to the actual height of your sight and you will have the correct height of the replacement sight.

Example
At 100 yards, your shot is 6" low and the distance between your front and rear sight is 19.5".

6 X 19.5
= .0325
3600
Since you are shooting low, you would need to lower your front sight by .032".

* For rifles, you measure the front sight height from the bottom of the dovetail to the top of the sight. For pistols you measure the height of the blade only. This is true unless stated otherwise in the sight specifications.”

If you don’t like doing math, you can just type the numbers in here.

https://www.brownells.com/aspx/learn/learndetail.aspx?lid=13093
 
m/(r/s)
m=how much you want to move the impact
r= the range
s= the sight radius

In this instance... 10 yards divided by 6” = 60
3” divided by 60 = .05

Roughly speaking, depending on the sight radius.

Wyman

ETA, or the easiest way... Tap and shoot. Tap and shoot. Repeat until satisfied.
 
Make a fine pencil line on the sight and frame. Tap it. (to the left)Some things in Life are not that complicated.:)
Be sure it is not operator error and have the gun in a fixed rest, so now you need to buy a ransom rest.;)
 
Go ahead and be amused at the concern for accuracy. Meanwhile, I'll be hitting stuff with a 1911 at ranges you apparently reserve for rifles.
 
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