Math question for you guys

[foob]

My rifle's POI is about 15 inches above POA, at 100 yards. How high should I raise my front sights (maybe fabricate a new one), to get POI=POA.

The distance from rear sight to front sight is 22.5 inches.

 

[eliphalet]

sounds like you need to move the rear sight up to me , but maybe I read your post wrong.
to sight in with iron sights you move the rear sight the direction you want the bullet to move and the front the opposite direction you want the bullet to go.

 

[foob]

I want the bullet to move down. You have it reversed.

 

[budney]

You move the rear sight the same way you want the group to move, in this case down.

 

[Shear_stress]

Approx. 0.094", all else being equal.

 

[foob]

Thanks Shear_stress. I found tngunparts sells taller M39 front sights. Just bought one. I can trim it as I shoot it.

budney, can't move rear sight down, it's at the lowest point.

 

[Vaarok]

Try different ammo weights, too...

 

[foob]

I tried both hungarian heavy ball and czech silver tips, both about 15". Czech silver tips definitely group better, I'm getting 3" at 100 yards, second time shooting. Hungarian heavy ball is giving me 6" groups.

I'm going to try a few hungarian light ball, see how it goes.

 

[budney]

budney, can't move rear sight down, it's at the lowest point.

Right. I realized that; I didn't want to confuse things by switching from rear to front sight.

--Len.

 

[Eightball]

I'm just curious.....what are you shooting?

 

[rangerruck]

sounds like a mosin, i would say that a 15 inch drop is not that much at all, but def get a backup front site. I was going to say, take off an 1/16, then see what happens.

 

[richardschennberg]

Rear sight adjustment = 15 inches x 22.5 inches / 100 yards
= 15 inches x 22.5 inches / (100 x 3 x 12) inches
= 15 inches x 22.5 / 3,600
= 0.094 inches
Shear Stress had it right, I just thought I'd show you how to calculate it:
Read sight adjustment =
aimpoint change on target x distance between iron sights / distance from front sight to target.
You have to convert the distance between iron sights and the distance from front sight to target into the same units.
In this case there were 3 foot per yards and then 12 inches per foot
(100 yards = 100 x 3 x 12 inches = 3,600 inches).
Richard
Schennberg.com

 

[351 WINCHESTER]

Prior to your post I was going to recommend installing a taller front sight to move the poi down. I was going to guess about 1/2" to start. I had a similar problem with my no 5 enfield. It was shooting low. I finally found a -.015 front sight and she's much better.

 

[foob]

Funny thing is the front sight was a 79 put the Finn armorer replaced it with a shorter 71 (number crossed out on barrel to show replacement). Maybe they don't zero at 100 yards.