The MOA Formula For Calculating MOA Clicks For A Shot Less Than 100 Yards If Zeroed At 100 Yards?

A

adn258

New member
So I'm just learning the basics of longer range shooting. I know 1 MOA is 1.047. So if you're looking a ballistics chart and ABC round is zeroed at 100 yards but has a 6 inch drop at 200 yards (hypothetically)

You would take (1.047*2) = 2.094 and then 6/2.094 2.86MOA. Let's round up and say 3 MOA so if you had a 1/4th MOA per click scope you would want to adjust up 12 MOA or 12 clicks.

Alright, that all makes sense, but let's say we take the following ballistics image of 10mm auto for example:

imageproxy.jpg


This is for a gun zeroed at 100 yards using 10mm. Alright, let's say I did that, and I know 50 yards would likely be smarter using 10mm but just for the sake of argument.

The gun would be shooting way too high at 25 yards if it were zeroed for 100 yards given the fast drop of 10mm auto. It looks like the bullet has an 11 inch drop almost from 25 yards versus o 100 yards.

So I'm guessing 25 yards 1.047/4=0.261MOA so if I wanted to adjust elevation DOWN to compensate for the closer distance it would be 11/0.261 = approx 42MOA but on a 1/4thMOA per click scope that means you would need to adjust 168-169 clicks down....this can't be right or is it?

What am I missing here? Thanks for your help guys as I learn this stuff!

What is the correct way to calculate this?
 
Get some paper and make drawings. Its easier to see.

A major point to consider ,particularly at closer ranges,is sight height above the bore.
Lets not go off to the weeds.but if your sight height is 1.5 inches, Remember your 1/4 moa clicks are good for about 1/16 in each at 25 yds.

The bullet begins to fall,per Gravity,as soon as it leaves the muzzle,relative to the line of the bore. The bullet does nor "rise" above the line of the bore.

The line of sights is a different line. Lets forget the curvature of the earth for now. Lets go "Flat Earth". If we set the bore dead level horizontal,the bullet moves toward earth at the acceleration of gravity as soon as it clears the bore.

We depress the line of sights downward to intersect the path of the bullet Remember we adjust line of sight to intersect line of bore at two points down range. I hesitate to use "Up" and "Down" without clarification.

The first intersection typically occurs at a relatively close range.It might be 25 yds,or 35 yds. This range is greatly affected by sight height. Sight height may be 1/2 inch on a handgun or 2 1/4 on a rifle.

Once the bullet path intersects the line of sight,it travels above the line of sight until gravity pulls it back down through the line of sight.


So it might happen that the gun shoots slightly low till about 25 yds,then it will gradually shoot higher on the target till max midrange trajectory, then it will fall till it passes through the target at sight in range. After that,the bullet is dropping below the line of sight. Look at the "Path" column in your chart.

Back to your initial question about calculating short range corrections

The bullet strike on a 100 yd target will be at the second intersection of the line of sight and the line of bullet path.

The closer "sight in distance" at 25 or 35 yds,+ or - is the first intersection of line of sight and path of bullet.

Given you are sighted at 100 yds and your sight height is fixed,those two facts determine the exact range this close sight in occurs.

The calculation is in the proportional nature of trig and geometry.

But you posted a printout from ballistic software. The easiest way is to just plug accurate values in your software ,particularly sight height,and run it.

If you are shooting an iron sighted handgun,your 1.5 in sight height will mess up your results .Measure!

Also,don't let the "drop" number confuse you. Thats total drop based on time of flight from he line of the bore.

I think you will find that with a 100 yd zero,you sights will be very close to "on" at 25 yds.
Note in your "Path" column your bullet will strike about 2.4 in high at 50 yds

Also,you can change parameters in your software. Your "max range" is set on 500. Try reducing it to 200.

Then reset "interval" to 10 yds. Or,even 5 yds. Then run it again.
 
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HiBC said:
Get some paper and make drawings. Its easier to see.

A major point to consider ,particularly at closer ranges,is sight height above the bore.
Lets not go off to the weeds.but if your sight height is 1.5 inches, Remember your 1/4 moa clicks are good for about 1/16 in each at 25 yds.

The bullet begins to fall,per Gravity,as soon as it leaves the muzzle,relative to the line of the bore. The bullet does nor "rise" above the line of the bore.

The line of sights is a different line. Lets forget the curvature of the earth for now. Lets go "Flat Earth". If we set the bore dead level horizontal,the bullet moves toward earth at the acceleration of gravity as soon as it clears the bore.

We depress the line of sights downward to intersect the path of the bullet Remember we adjust line of sight to intersect line of bore at two points down range. I hesitate to use "Up" and "Down" without clarification.

The first intersection typically occurs at a relatively close range.It might be 25 yds,or 35 yds. This range is greatly affected by sight height. Sight height may be 1/2 inch on a handgun or 2 1/4 on a rifle.

Once the bullet path intersects the line of sight,it travels above the line of sight until gravity pulls it back down through the line of sight.


So it might happen that the gun shoots slightly low till about 25 yds,then it will gradually shoot higher on the target till max midrange trajectory, then it will fall till it passes through the target at sight in range. After that,the bullet is dropping below the line of sight. Look at the "Path" column in your chart.

Back to your initial question about calculating short range corrections

The bullet strike on a 100 yd target will be at the second intersection of the line of sight and the line of bullet path.

The closer "sight in distance" at 25 or 35 yds,+ or - is the first intersection of line of sight and path of bullet.

Given you are sighted at 100 yds and your sight height is fixed,those two facts determine the exact range this close sight in occurs.

The calculation is in the proportional nature of trig and geometry.

But you posted a printout from ballistic software. The easiest way is to just plug accurate values in your software ,particularly sight height,and run it.

If you are shooting an iron sighted handgun,your 1.5 in sight height will mess up your results .Measure!

Also,don't let the "drop" number confuse you. Thats total drop based on time of flight from he line of the bore.

I think you will find that with a 100 yd zero,you sights will be very close to "on" at 25 yds.
Note in your "Path" column your bullet will strike about 2.4 in high at 50 yds

Also,you can change parameters in your software. Your "max range" is set on 500. Try reducing it to 200.

Then reset "interval" to 10 yds. Or,even 5 yds. Then run it again.
Click to expand...
I see what you mean and thanks so much for this awesome reply. Basically, at these shorter ranges there are way more factors to consider than some math formula at the 100 yard zero.
 
If you are sighted at 100 yds, try just shooting it at 25 yds. You might be surprised how close it is.

And you might make note of (take a picture) your 25 yd target,or find the exact range your 100 yd zero has a perfect "up close" zero.

Thats real handy next time you need to sight in.
 
With MOST scopes 1 click = 1/4" at 100 yards. At 50 yards you need 8 clicks to equal 1". At 25 yards you need 16 clicks to equal 1"

The better scopes are pretty accurate, but many scopes are not. Even many name brand scopes in the $300-$400 price range will be inaccurate. You may find that at 100 yards you need anywhere between 2-6 clicks to move your POI 1". That is why you have to actually go out and shoot to see where bullets are impacting.

And not all scopes are 1/4MOA adjustable. Some are 1/2 MOA meaning you need 2 clicks to move POI 1" at 100 yards. Four clicks at 50 yards and 8 clicks at 25. This is more common on low powered scopes intended for close range brush guns and handguns.

And then there are scopes with Mill adjustments. With those you need 3 clicks to move POI 1" at 100 yards. Be sure to read the specs on the scope you are using.
 
There is "true" MOA, which is 1.047" at 100 yards and "Shooter" MOA which is 1" at 100 yards. Scope makers mix and match and really screw up the math. Most actually use a 1/4" or 1/2" clicks at 100 yards. Then when they use true MOA on the reticle, even more complicated. Close enough for most out to 400 yards or so, but past that, it gets messy and the errors grow. In the old days, you zero'd at 100, then confirmed your DOPE at 200, 300, 400, etc (yards or meters) to build an actual range card. The software engines all use true MOA and that won't match most MOA scopes in their click adjustments. Some software allows you to mix units up to match your actual scope.

You have to know what the scope manufacturer actually used. IPHY, true MOA, Shooter MOA. One reason a lot of long range shooters just skip it all and move to Mils, which is base 10, and easier, more accurate math. Still an angle, just easier.
 
An IPHY gives you 10 inches on the target at 1000 yards, right?
A geometric MOA gives you 10.47" on the target.
I have seen Long Range Benchrest shots where a half inch mattered, but in any other use, it is hard to see a difference.

Mils? Are you using geometric mils, artillery mils, or infantry mils? Russian mils?
 
Jim, yes, IPHY, as used by scope manufacturers is supposed to be 10" at 1000 yards.

400 yards and less, it is probably impossible to measure the error. Still slight out to 1000 yards, yes. But the error is not linear, so it does compound.

Scope manufacturer's use Milradians. 1 mil is 1 yard at 1000 yards, or 1 meter at 1000 meters.
 
The 10mm gun, zeroed at 100yd, shoots 1.18" high at 25yd. 1.18" at 25yd is 4.5 MOA. If you really want to change the gun's zero from 100yd to 25yd, you need to lower the elevation by 18 clicks.

-TL

Sent from my SM-N960U using Tapatalk
 
A tip given to me by an old optics repairman, when adjusting your scope, go 2-3 clicks PAST where you want, and then come back.

He said this minimizes the "backlash" in the adjustment mechanism.

Can't say if he was right, but I've seen nothing to prove him wrong...:rolleyes:
 
Just to simpify things, if you are going to do your calculations in MOA, don't switch back and forth from MOA to inches to MOA, just do all your calculations in MOA. You will avoid a lot of confusion. Your scope has 1/4 MOA adjustments, you need to just figure out your MOA drop and determine how many 1/4 MOA clicks you will need. And for shots under 100 yds, just point and click.
 
Scope manufacturer's use Milradians. 1 mil is 1 yard at 1000 yards, or 1 meter at 1000 meters.
Click to expand...

Depends on your definition of "is." A Milliradian subtends 1/1000 of the radius on the arc. But the target is usually flat so you have the difference between the arc and the chord. Not much for very small angles, normally disregarded.

The angular circumference of a circle is 2 Pi Radians, so there are 6.2832 radians around a circle, 6283.2 milliradians. Call that the geometric mil. The infantry used to round it off to 6280 mils in a circle, the artillery used 6400 which got standardized across NATO. The Russians thought 6000 was close enough.
Which one do the scope makers use?

True, there is only 1.8% difference between a NATO mil and a geometric mil while there is a 4.7% difference between IPHY and minutes of angle, so the mil IS more precise and is very convenient if you are using the French system where a 1000 multiple is built in.
 
Jim, I have not seen any scope manufacturers use the anything other than 1 mil as 1 yard at 1000 yards. Let's not confuse an already confusing subject.

That is why long range shooters use Mil scopes in most cases (F class being an exception due to target measurement). The hardware matches the software. In MOA, it is rare that the hardware matches the software.
 
Use the USA National Shooting Sports Federation standard of one inch per hundred yards. Makes the mental math issue easy. Especially when using targets whose rings are spaced in inches.

Besides there can be a 4.7% spread in the scope's image size the fixed adjustments move the reticle around in. All lenses have focal length tolerances. That'll be effecting click values on targets.
 
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Tangolima:

The 10mm gun, zeroed at 100yd, shoots 1.18" high at 25yd. 1.18" at 25yd is 4.5 MOA. If you really want to change the gun's zero from 100yd to 25yd, you need to lower the elevation by 18 clicks.
Click to expand...

I'm sure you gave a good faith ,calculated answer. Good Man!

What my problem is,I don't know if he is shooting an iron sighted Glock or an optic equipt PCC. The sight height is a key component in the calculation. (As I suggested in my post)

Common Olde Tyme advice for the Wily Nimrod sighting in at the range for deer season was sight in dead on at 25 yds and you should be (maybe) on paper at 100 yds. A lot of folks call the 25 yd sight in good to go,and they go hunting with it.

IMO, Its good to plug all the data in to the calculator and get a result. But then,given he;s sighted in at 100 yds, I would not change the sights.I'd shoot a target at 25 yds. I'd see what I got. I'm thinking it will be pretty close.
 
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Bart B. said:
Use the USA National Shooting Sports Federation standard of one inch per hundred yards. Makes the mental math issue easy. Especially when using targets whose rings are spaced in inches.

Besides there can be a 4.7% spread in the scope's image size the fixed adjustments move the reticle around in. All lenses have focal length tolerances. That'll be effecting click values on targets.
Click to expand...
Exactly the mess that was created and confuses people. Don't be part of the problem.
 
And the difference between an IPHY and a geometric MOA wasn't confusing enough.

But then zeroing a 10mm at 100 yards was pretty confusing to start with.
 
But then zeroing a 10mm at 100 yards was pretty confusing to start with.
Click to expand...

It depends. Out to 100 yds,its never more than 2 1/2 in high. I can see better with a 6 oclock hold.
Its about 4 in low at 125 . IMO,its a pretty useful sight in.

If you practice 100 yd handgun shots,you can get confident in 100 yd handgun shots.

You can't make the shot if you don't take the shot.

I'm not an especially good shot,but with the freedom of a large private ranch.I've enjoyed a lot of "rock and bush shots" way out yonder.

Try holding up some blade at 300 yds. You might have fun!
 
European sights often use the metric system. Typically 1 click moves LOS 2 mm on target at 50 meters.

Convert that to inches and MOA at 100 yards.

For all the perfectionists, use this value for MOA to over a hundred decimal places...

1.04719753642832854694747069666400334739860873986429
830552235157457471965151538005004775737357536725837... inches per 100 yards.

It's still not exact. But the best medicine for those who want to be.

Remember that the scope adjustments for windage and elevation only move the line of sight direction and angle.
 
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Bart,in case you have not noticed,My response has been to the OP regarding a 100 yd zero,a 10 mm,and a 25 yd target.

I'm not all that good at anything. If I'm looking through a spotting scope I can say" You were about 6 in right and 3 in low" .....on a good day.

Best is having a target on the bench with a pointer, but I never have seen a co-ordinate measuring machine,a Cord-Ax ,toolmakers microscope,etc at the range,

I'll agree,if you are using a mil reticle,mil adjustments are good.

For a hack like me,ever changing factors like wind and mirage sort of make 1.000 versus 1.047 in the category of"noise"


But,as a spectator,the discussion is good. Somebody has to be "right" after all!

I don't generally get the .0001 indicator and the gage blocks out when I'm working with wood.

I am in a circle with some of the long range precision shooters. I don't shoot the game. I am amazed at just how good the Kestrel and softwares can be,
Amazing!!

But even the optics of the air is a variable,. At some point,a fellow has to take the step from what we expect to looking at what we get. Thats real.

Even with precision machine tools
 
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