How far to drift rear sight for 1" at 25 meters?

[wherermykeys]

I'd like to adjust my POI about an inch to the right at 25 meters. Does anyone know roughly how far I need to drift my rear sight for that? I can't really do it at the range so I'd like to hopefully get it right at home before I head out.

 

[tjhaile]

With all units in inches, mm, or whatever:

Impact change/range = sight adjustment/sight radius

Therefore:
sight adjustment = impact change*sight radius/range

For example:
You want to move your point of impact 1" right at 25m and your sight radius is 7". This means that your rear sight would have to be moved right by:

1(7)/(25*39.37) = .007"

 

[foxytrapper]

Drifted the rear sight on one of my 1911's last week. The best way to sight in yer shootin iron is at the range. I took the tools required and did her on the bench.

 

[wherermykeys]

With all units in inches, mm, or whatever:

Impact change/range = sight adjustment/sight radius

Therefore:
sight adjustment = impact change*sight radius/range

For example:
You want to move your point of impact 1" right at 25m and your sight radius is 7". This means that your rear sight would have to be moved right by:

1(7)/(25*39.37) = .007"

Awesome, thank you!

 

[wherermykeys]

woah, hang on, that's it? That's like the width of a hair! Not being ungrateful but are you sure that formula's correct?

 

[wherermykeys]

Drifted the rear sight on one of my 1911's last week. The best way to sight in yer shootin iron is at the range. I took the tools required and did her on the bench.

What tools did you use at the range? I was going to use a vice and jimmy up some kind of pusher with a c-clamp...

 

[Short Knife Johnson]

Nope, that sounds about right. My silhouette rifle has a 30 inch sight radius. To move the point of impact 1 m.o.a. is around .001" movement of the eycup. That's a 4 minute change is what you need.

 

[Ganderite]

I estimate about 1 mm.

the easy way to see a change is to put a dab of WhiteOut (typo correcting fluid) on the sight base and frame. When it is good and dry, just draw a scribe mark with a pen or pencil. Any movement will be obvious. After the project, it scrape off with a fingernail.

 

[tjhaile]

woah, hang on, that's it? That's like the width of a hair! Not being ungrateful but are you sure that formula's correct?

It doesn't take much! I'll admit that I double checked it myself, but, if you think about it, a triangle with one angle of 4 minutes is a pretty pointy triangle.

The sight radius and the amount you want to move the sight form the legs of a right triangle with the same angles as the one formed using the change in impact and the range. The angle is the same, so we simply use the ratio of the tangents (opposite leg/adjacent leg) to solve for the unknown, in this case, sight adjustment.