Front Sight Height Calculator

[Mark Elliott]

If anybody is interested, I spent this morning creating a spreadsheet to calculate the proper height of a front sight for a given sighting in situation. It is an Excel spreadsheet. You replace the values in Bold print. Everything else is locked. Take a look at it and see if you can use it. If you mount your sights centered on the flat with the front sight height as specified by this calculator, you should be pretty close, if not in the black, when you go to sight in. Of course, you do need a good idea of the muzzle velocity of your load. You can use the Lyman reference, but I don’t think you can go to wrong by assuming 1500f/s.

http://www.markelliottva.com/wordpress/wp-content/uploads/downloads/SightCalc2.xls

Best

Mark Elliott

[mjm46@bellsouth.net]

Thanks Mark that's very cool.

A couple of questions.

What is "sight radius"? Does that refer to the target?

Is this formula designed to a specific caliber? Wouldn't bullet drop vary by caliber?

Sorry, but you knew there would be questions. But I really like it.

[Mark Elliott]

The sight radius is the distance between the rear and the front sights.  I measure between the rear surface of the rear sight to the rear of the front sight. 

 The caliber has nothing to do with the calculation except that it will affect the muzzle velocity given the same powder charge.  You need to use the load tables to determine the approximate muzzle velocity of your load.  Given the extreme mass of the earth,   the mass of a falling object is irrelevant with regard to its effect on gravitational attraction.   Therefore, the acceleration due to gravity is considered a constant for all falling objects on the earth.   Remember the experiment with the feather and the canon ball.  They both fall at the same rate; ie... the acceleration due to gravity of 32 f/s^2 or 9.81 m/s^2.    Now given that force=mass x acceleration,  the force (the weight) exerted on each object by gravity is very different.  In other words,  the canon ball will make a bigger dent in the ground when it hits than the feather. 

I hope that helps explain things better.   The calculations I use are pretty simple physics and trig calculations.   I do make simplifying assumptions such as ignoring wind resistance and that fact that the bullet travels in an arc as opposed to a straight line.   The purpose is to get the front sight height very close to the final sighted in height without making it too short.   I want to be close to the black on the first shot as opposed to completely outside the target area  completely.   

In the past,  I have just made these calculation on paper went I made the front sight.   This time,  I decided to make a spreadsheet to do the calculations and uploaded the spreadsheet to my iPhone to run under the Spreadsheet app.   Using these calculations, it usually takes me five shots to get solidly in the black which is as much as I do on any rifle I sell.    I always sights with the same load; ball .005" under bore, .020" ticking patch pre-lubed with a dried Ballistol/water mix(1:7), and a charge 1.5 times the bore.   I use FFFG for 45 caliber and under, and FFG for 50 caliber and over.

[mjm46@bellsouth.net]

Thanks Mark. On the drop, I know that mass does not affect the pull of gravity. But I was wondering if the bullet diameter might affect drag and cause it to slow and then the impact point would be lower because of the drop being longer. A drastic example would be an .32 cal and a .75 cal both with an exact same muzzle velocity, wouldn't the .75 cal drop more, because of drag, or not?

This info is at a perfect time for me, I'm about to put new sights on my rifle.

[Mark Elliott]

There would be more air/wind resistance but there is also more momentum to overcome it.   I just ignore  the whole issue to simplify the calculation.  Again the point is to get close to the final setting.

[Acer Saccharum]

This is really cool, Mark.

I do think it should be in Black Powder Shooting, but it should stay here for a while, so everyone sees it, then I'll move it over there.

Tom

[NSBrown]

Mark, this is timely for me also. Thanks. I feel like I just got an excellent class lecture from J. P. Beck...except for thr iPhone app bit. Thanks for sharing.

Stewart Brown

[Mark Elliott]

I think even JP Beck would have an iPhone if he were alive today.

Everybody,  please let me know if you find any errors in my calculations.

Thanks,

Mark E.

[Mark Elliott]

I should also mention that I assume the bore is straight and the profile of the barrel is symmetrical.   If it isn't, all bets are off.  Of course, usually it is, or close enough.   

[ironwolf]

Great info Mark.  I've always calculated sight height, using a ratio equation, for a 4" drop at 100yds. on a new build, just to get on the paper.   This formula should be much mo better.

  It's interesting to note that if you could drop a roundball and shoot a roundball at exactly the same time, they would hit the ground at the same time.

    Kevin

[Curtis]

Pardon the pun, Mark, but I will give your calculator a shot when I site in the next rifle.  Thanks for sharing it! 

Curtis

[garra]

Mark,

New member here.  I was looking for information on how to determine sight height.  I just purchased a muzzleloder with a missing rear sight, trying to figure out how to determine what I need.
Maybe I can use your calculations backwards and get close.

regards,

gg

[garra]

Mark,

Back again.  Tried your calculator.  I just keep changing the rear height until the answer appeared to match my existing front sight.  Neat!!!!!    Told me I needed a rear sight minumum height for 50 yards of .250 based on my barrel diameters and radius.  I have a new to me 32 caliber percussion, made about 1850, my first muzzleloader.  Great spreadsheet, really appreciate finding something to answer my question.
Now I can plug in different ranges on available sights to see how they match for different distances, great tool!!
regards,

gg

[Mark Elliott]

I had been informed some time ago that the calculations in my sight height calculator were off.   I finally got around to looking at it again and I think that I have addressed the deficiency.   It would seem that I neglected to take into account the offset of the line of sight from the center of the bore.   Actually,  I really never thought it made much difference, but I have taken it into account in the new calculations.   You will notice in the updated spreadsheet that I have added an number of interim calculations related to the line of sight offset.   If the new calculations are correct, then using the sample values, you would have needed to take an additional .011" off the front sight.  I am sorry for the oversight.

[Collector]

Back to all that physics stuff; that whole feather, cannon ball and dropping and shooting the round ball... all occur in an absolute vacuum and you have to square the rate of acceleration (acceleration X acceleration,) in the formula for force, to get the right answer. 

Mark, anything that helps us save time and our resources is a great help.  Thanks!

[Mark Elliott]

I am still being told that my calculations are incorrect by a person who has his own calculator for sale, but I am not being told exactly why.   So,   I would suggest that my calculator be ignored.  Of course,  if someone would like to explain to me why and how it is wrong,   I would be more than happy to listen.   

Thanks,

Mark E.

[Mark Elliott]

   Ok,  I took another look at my calculations and FINALLY saw the real problem.    No one could possibly have explained why my calculations where wrong because no rational human being could possibly understand what I did.    I don't fully, and I am the one who did it.    Basically,  I failed to comprehend the difference between velocity and linear position.    See,  I told you it was incomprehensible.    Basically,  my mind has turned to mush.    Just a few short years ago,  I could still do integral calculus with ease.   Now, apparently,  I don't even understand the concepts anymore.  That said,   I have reworked the calculator and my results are in alignment with what I was told they should be.   I do, however, now feel that a muzzle velocity of 1500f/s is too high for most loads.   I think 1200f/s might be more appropriate for standard hunting loads, but please consult the Lyman manual.   

I most humbly apologize for any inconvenience this may have caused.