Math Formula to go from 50 yards to 100 yards

[Paul L]

Hi,

Can one of you smart people post the formula to calculate how high a rear-site should move when going from 50 yards to 100 yards? That would get me in the ball-park to begin fine tuning at the range.

Thanks!

Paul
15th Virginia Cavalry

[Rob FreemanWBR]

Paul,

As a knuckle dragger - I quote Barbie when I say,"math is hard".

But re your question, there is no one calculation that can be applied to the myriad of arms. I know one variable involves the pieces respective sight radius.

If you do have the correct sight radius, then yes you can adjust the location of your peep/rear sight. I have seen and leafed thru "the book" a massive, bound, printout giving the exact sight settings given the distance needed to raise or loser a shot group based on distance/yardage and radius. From looking at the compendium of rows and columns of numbers, someone had a LOT of time on their hands, and unlimited access to a program/computer and dot Matrix printer.

But as guys with slide rules and 30 pound brains say, "the math is good", I.e. The Excruciatingly detailed measurements are on the money.

Now if if you want to talk about MoA...

Sorry if I didn't fully address your question, but I'm sure other more technically inclined folks will be happy to help!

[P.Altland]

Or you can try this Formula:

Amount of Error X Sight Radius/Distance
= Sight Correction Needed

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

6 X 19.5/3600 = .0325

Since you are shooting low, you would need to lower your front sight or raise the rear by 0.032".

REMEMBER ALL MEASUREMENTS MUST BE IN INCHES.


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[Chris Sweeney]

Or you can try this Formula:

Amount of Error X Sight Radius/Distance
= Sight Correction Needed

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

6 X 19.5/3600 = .0325

Since you are shooting low, you would need to lower your front sight by .032".

REMEMBER ALL MEASUREMENTS MUST BE IN INCHES.


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This formula tells you how much you need to move your sight to be on target at a specific distance. What I think you are asking is "If I know where my gun shoots at 50 yards, how do I know where it will hit at 100 yards?"

Unfortunately, there is no general correlation. It depends on:

Bullet weight
bullet ballistic coefficient
height of sights above the barrel
muzzle velocity, which is determined by powder charge, barrel length, type of powder and a bunch of other things.


There are ballistic tables that can estimate trajectory based on the above. for example:
The 315 grain Lyman semi-wadcutter at 700 fps, zeroed at 50 yards has a theoretical drop of almost 21." The same bullet at 800 fps MV would drop 11 inches and change.
The old standby lyman 575213 is predicted to drop just shy of 14" at 800 fps velocity. Of course YMMV. Widely!

So, to make a long story even longer, the only good way is to shoot it at 100 yards, measure the distance between where you aimed and where you hit, then apply the above-mentioned formula.

Remember the FORS rule (Front Opposite Rear Same); if you want to raise THE POINT OF IMPACT, you would either lower the front sight or raise the rear sight- and always start off with a sight way higher than you think you need, and never make all the correction in one round of filing- I know this from learning a very expensive lesson (repeatedly) to wit: it is way easier to file metal off than it is to file metal on!

[P.Altland]

The OP is asking for exactly what I'm giving him. He is asking for the sight correction formula so that he can make a rough adjustment to his rear sight @ 100 yards. Then to be followed up with fine tuning. Please read it again.
Zero your gun @ 50 yards. If you have a long range style rear sight (aka '55, Mississippi, Enfield) shoot 100 yards using your 50 yard sight. Measure point of impact from center of target and do the math. Raise the rear by your result. If you have a leaf rear, then the 100 yard leaf needs to be taller than the 50 yard leaf by amount in result.
BTW, I did say lower front or raise the rear.



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[C.W. Artillery]

SIGHT ADJUSTMENTS



19 September 2016

Any instructional information on the subject of gun sights and the adjusting of same is somewhat incomplete with out the information of "wind drift". The original question does seem to be directed at the bullet drop (gravity) when moving to a target placed at a farther distance.

The longer time period that the bullet is in flight, the great the affect of cross wind (excluding head wind and tail wind for the moment). So the shooter must not only adjust the rear sight to achieve elevation of impact on the target, the shooter must also account for the increase in bullet drift due to the longer "time in flight" period to which the bullet is subjected to side wind.

Webb Brown
First Maine H. A.
(Retired)

.

[jonk]

While wind drift is certainly a factor in any shooting discipline, given the relatively short ranges and heavy bullets we use, it really isn't that much; nor is there anything you can do about it other than use KY windage.

As to the formula, its a VERY rough ballpark tool, useful to get you on paper- hopefully. There is a HUGE difference in calculating 100 yard zero based on 50 yard zero with a 500 grain full wadcutter and say a 575213, that's balistically fairly decent... huge difference depending on velocity and powder charge too. For instance: while I usually shoot a Hodgdon 400 gr bullet at both ranges, if I shoot the little 315 gr minie at 100, it will shoot about a foot high with the same powder charge. If I shoot the 575213, it will shoot about 6" low. That's an extreme range of 18 inches, simply due to different bullet weight and ballistics.

[P.Altland]

Bullet weight has nothing to do with what the OP is asking. Pick the bullet your going to shoot based on what groups best and then use the formula. It's very simple and works. Why does everyone want to over-complicate it?


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[C.W. Artillery]

. . . . . . . . . given the relatively short ranges and heavy bullets we use, it really isn't that much; nor is there anything you can do about it other than use KY windage.

I feel that if you were experienced competing on standard American "ring targets" printed on paper your conclusion and rational would be decidedly different. Consider if you will, that the skirmisher's target increases in size as the shooting distance becomes greater. For example, the clay pigeon is relegated predominantly to 50 yards distance, and the 6" X 6" is used at 100 yards.

In other rifle shooting disciplines which are shot on paper, the bulls eye (read "X") is approximately the same diameter for 100 yards vis-a-vis 200 yards. I should also point out that fold down Vernier tang sights certainly do have screw adjustable windage features, as do front globe sights have these features, in which case they are known as "Windgage Front Sights".

The sights that I mention are, of course, from a later period when the Buffalo hunters were earning their living out on the plains using center fire technology.

Regards,

Webb B.

[lmcmahon]

try this website for figuring sight measurements.
http://www.sdmfabricating.com/sightcalc.html

[Paul L]

Thanks for all the responses! The bullet and powder charge will not change between my 50 yard and 100 yard ranges. I thought there might be a relatively simple calculation to get me in the ball park for raising the rear sight before getting to the range. I guess I will just have to go and adjust the rear sight as I fire the rounds.

Thanks!
Paul
15th Virginia Cavalry

[P.Altland]

Thanks for all the responses! The bullet and powder charge will not change between my 50 yard and 100 yard ranges. I thought there might be a relatively simple calculation to get me in the ball park for raising the rear sight before getting to the range. I guess I will just have to go and adjust the rear sight as I fire the rounds.

Thanks!
Paul
15th Virginia Cavalry

There is. Don't be discouraged by all the posts. Use the web based version that Linwood provided or the one on Brownell's site. Both are based on the same formula I gave at the beginning.


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[bobanderson]

As to the formula, its a VERY rough ballpark tool, useful to get you on paper- hopefully. There is a HUGE difference in calculating 100 yard zero based on 50 yard zero with a 500 grain full wadcutter and say a 575213, that's balistically fairly decent... huge difference depending on velocity and powder charge too. For instance: while I usually shoot a Hodgdon 400 gr bullet at both ranges, if I shoot the little 315 gr minie at 100, it will shoot about a foot high with the same powder charge. If I shoot the 575213, it will shoot about 6" low. That's an extreme range of 18 inches, simply due to different bullet weight and ballistics.

Careful, John. Bullet weight and ballistics are not a factor because you are correcting bullet impact point on the 100 yard target. For this to work, you shoot at the 100 yard target with your 50 yard sights and calculate the change.
Of course, the very first step in this process is to find the best grouping load at both distances. Only then do I break out the files.