I am going to have JJ make a new front sight for my Harkom 450BPE. It will be one of his small bead Warthog Ivory sights.
The gun is shooting fantastic groups at 1756-1780fps. The groups are just 12" high at 100yds. The current front sight measures .075" high from the rib to the top of the bead.
I shot some groups today with a section of a 8-penny nail taped to the top of the blade. This made the sight .180" high, to the top of the bead...it shot 8" low.
By these groups, I am thinking that I should have the new sight built at .138" to the top of the bead. This is based on the point of aim setting on top of the bead.

Here is my logic: I subtracted .075" from .180" and got .105" difference in sight height...which is equal to 20" difference in bullet impact height. Then multiplied .105 x 8" needed to rise from the .180" sight...and divided by 20" total impact difference. This is simple algebra...cross multiply. This gave me .042" needed to gain the 8" on the target. I subtracted the .042" from the .180" blade with nail bead height to get a .138" high sight needed.

Does this make since? Is it that simple, or am I all messed up in my thinking. Is there some other formula used for figuring this? It seems like a general formula would be poor, at best due to different recoil characteristics of different doubles. My equation simply used real sight height versus real groups printed.

Any suggestions would be appreciated.
Thanks, ND

Nitrodave,

The amount of sight movement required is based on similar triangles. One for your sight radius and one for your target impacts at a given distance. You did not mention your sight radius.

For example, if your sight radius is 18" and your target is 50 yards (1800") away, a 0.010" difference in sight height will move the impact 1" at 50 yards. This works for windage as well.

So, if your sight radius is 18" and your target is 100 yards (3600") away, a 0.005" difference in sight height will move the impact 1" at 100 yards.

This works for your specific rifle since you have measured how far off your POI is from your POA for this load fired in this rifle.

Since your rifle is shooting high, you need either a higher front sight or a lower rear sight.

If you prefer, set it up as a proportion.



Sight Radius (inches)
__________________________ = Y

Target Distance (inches)


Where Y = Amount to change sight to move
the POI 1" at the target distance.


Hope this helps you.

Bwana_Dave,
Thanks! That confirms my thinking. I calculated it as a ratio...we basically used the same formula. Your formula is working off sight radius and mine is working off of total height of the front blade...same/same. When I punch my numbers into your formula, I get .040" and when I figured it my way, I got .042".
I think a new front sight of .138" height off the rib, will be about perfect!
Thanks for the help, Dave