Thread: Calculating front sight height ? ( maths heavy )

Bigger brains than mine required for this one

I have just restored a Sharps 1859 Civil War Carbine
It still had the original carbine rear sight ( which is a very challenging POS )
I installed a circe 1873 front sight from another rifle
The rifle has passed proof and shoots an OK group considering the POS rear sight

But it is grouping 150mm above where I would like it to be

So here are the numbers

Range 25 meters

Group wants to shift Down 150 mm

Sight Radius is 530 mm

How do I calculate accurately how much to build up the front sight blade to lower the groups point of impact by the required 150mm

This will be a good formula to have on file because many of the old military and sporting carbines tent to shoot very high anyway

Cheers

Sight radius x elevation change required / target distance will be worth a try.
OR you could braze a lot on and keep filing and shooting till your happy

Originally Posted by akaroa1

Bigger brains than mine required for this one

I have just restored a Sharps 1859 Civil War Carbine
It still had the original carbine rear sight ( which is a very challenging POS )
I installed a circe 1873 front sight from another rifle
The rifle has passed proof and shoots an OK group considering the POS rear sight

But it is grouping 150mm above where I would like it to be

So here are the numbers

Range 25 meters

Group wants to shift Down 150 mm

Sight Radius is 530 mm

How do I calculate accurately how much to build up the front sight blade to lower the groups point of impact by the required 150mm

This will be a good formula to have on file because many of the old military and sporting carbines tent to shoot very high anyway

Cheers

Stuff the formulas, solution is to put a big zip tie on the barrel with the end being vertical.

Use it as a front post and keep cutting it till you get the right height.

Good luck.

Divide 25,000 mm by 530 = 47.17 (approx). Divide 150mm x 47.17 = 3.17mm front sight height change.

3.47769mm
Sorry. Just realised I used 25 yards, not meters.

Originally Posted by Marty Henry

Sight radius x elevation change required / target distance will be worth a try.
OR you could braze a lot on and keep filing and shooting till your happy

that would work fine
But this is a short term solution until i can get in a Marbles tang sight from USA and then I will likely make a full custom front globe

Originally Posted by gundoc

Divide 25,000 mm by 530 = 47.17 (approx). Divide 150mm x 47.17 = 3.17mm front sight height change.

@gundoc that is about what my instinct had been telling me

Very similar to my Rolling Block baby carbine which shot even higher with a shorter sight radius

So it will be a small piece of brass stuck on with Loctite 401

Thanks team

First job after lunch and I will post the point of impact results

Originally Posted by caberslash

Stuff the formulas, solution is to put a big zip tie on the barrel with the end being vertical.

Use it as a front post and keep cutting it till you get the right height.

Good luck.

I also like this idea of there is no existing front sight and you can choose from the hoard that is similar to the cable tie

Well that went pretty well to plan

Addition was 3.1mm once it was tidied up

Point of impact dropped 125 mm
So at 25m it's 75mm above the bill
This is likely to give a 75 to 100 m zero
And the bonus is the sight top is slightly narrower and a little easier to place in the rear sight V



It's the two big holes side by side and nearly touching



So it's all set up for a social shoot this weekend

And I also set up a cool portable shooting bench

Like the rifle...love the wheel barrow....

Originally Posted by akaroa1

Bigger brains than mine required for this one

I have just restored a Sharps 1859 Civil War Carbine
It still had the original carbine rear sight ( which is a very challenging POS )
I installed a circe 1873 front sight from another rifle
The rifle has passed proof and shoots an OK group considering the POS rear sight

But it is grouping 150mm above where I would like it to be

So here are the numbers

Range 25 meters

Group wants to shift Down 150 mm

Sight Radius is 530 mm

How do I calculate accurately how much to build up the front sight blade to lower the groups point of impact by the required 150mm

This will be a good formula to have on file because many of the old military and sporting carbines tent to shoot very high anyway

Cheers

It is all about proportions and ratios.

A sight radius of 0.53 m is about 1/50 of the distance to your 25m target.

So if the required change in impact is 150mm, divide this by 50 and you get 3mm.

I'll let you work out if you need to add or subtract the 3mm from the front sight height.

Originally Posted by Cordite

It is all about proportions and ratios.

A sight radius of 0.53 m is about 1/50 of the distance to your 25m target.

So if the required change in impact is 150mm, divide this by 50 and you get 3mm.

I'll let you work out if you need to add or subtract the 3mm from the front sight height.

Yes this is a good one to have on file
I will put this in the back of my Little Red Book
Don't trust these important things to memory

so a mm per inch isnt a bad rounded figure.