Need help with scope math... again

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josh3rd

josh3rd

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Apr 2, 2015
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Newark, Delaware, United States
A couple months ago I was helped by some of you members with scope math.

Okay if a scope is true at 10 power and I am shooting at 16 power what is the distance between Mill dots? And how do you get that math? And when doing that math how would I use it to say if I'm bracketing a brick that's 7 and 1/4 in Long at an unknown yardage how do I find out the math to find its distance. For those who answer this previously I am sorry because I lost the bookmark and I need you to chime in again. Thanks very much
 
Might this be the thread you lost?

Scope bracketing and true power level

I have a AirMax30SF and compete in HFT with a AA Prosport. First is it 10 or 12 power that it's, I guess the word is, "calibrated" for or for it's reticle to be 3.6" from center mildot to center of next mildot at 100yds? Secondly, after finding if it's either 10 or 12 power to be true at...
www.airgunnation.com www.airgunnation.com


Matthias 👍🏼
 
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JungleShooter said:
Might this be the thread you lost?

Scope bracketing and true power level

I have a AirMax30SF and compete in HFT with a AA Prosport. First is it 10 or 12 power that it's, I guess the word is, "calibrated" for or for it's reticle to be 3.6" from center mildot to center of next mildot at 100yds? Secondly, after finding if it's either 10 or 12 power to be true at...
www.airgunnation.com www.airgunnation.com


Matthias 👍🏼
Click to expand...
Scotchmo's reply was what I was leaning towards. But
Scotchmo said:
10x MIL-DOT at 10x: 3.6" @100yds
10x MIL-DOT at 16x: 2.25" @100yds

For a 7.25" brick @16X:
Distance(yds) = 7.25"/2.25" x 100yds/dots

FYI - The most common "brick" for mounting targets is a cinder block that measures 7.625", and don't count on the 16x mark being exact until you verify the actual spacing
Click to expand...

Scotchmo said:
10x MIL-DOT at 10x: 3.6" @100yds
10x MIL-DOT at 16x: 2.25" @100yds

For a 7.25" brick @16X:
Distance(yds) = 7.25"/2.25" x 100yds/dots

FYI - The most common "brick" for mounting targets is a cinder block that measures 7.625", and don't count on the 16x mark being exact until you verify the actual spacing for yourself.
Click to expand...
Cinder block was what I meant brother lol. Thank you for the correction and actual size. My other thing is how did come up with the 2.25" again?

Also would the 2.25" divided by 4 be what it is at 25yds?

Lastly, hopefully lol, do i range using the 2.25" for unknown distance if kept on 16x and I know my target's size?

Thank you before hand
 
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josh3rd said:
My other thing is how did come up with the 2.25" again?

Also would the 2.25" divided by 4 be what it is at 25yds?

do i range using the 2.25" for unknown distance if kept on 16x and I know my target's size?

...
Click to expand...
"My other thing is how did come up with the 2.25" again?"

On a particular SFP scope (and most mil-dot scopes), a mil-dot subtends 1 milliradian when the scope is set to 10x. A milliradian spans 3.6" at 100yds. The span of the mil-dot on an SFP scope is inversely proportional to magnification. So:

10x/16x x 3.6" = 2.25"

"Also would the 2.25" divided by 4 be what it is at 25yds?" - yes

"do i range using the 2.25" for unknown distance if kept on 16x and I know my target's size?" - yes
Pick the known size feature that you want to range on. Count the dot across the feature. Do the math to get a distance to target.

Mil-dots are designed to be read within 0.1 mil-dot. Easy to resolve to 1/2 mil-dot. Resolving to 0.1 mil-dot takes some practice. The larger the feature, the more dots it will encompass and the more precise the measurement (minimizes % error). At 0.1 resolution, a feature that spans 10 mil-dots would have a maximum 1% range reading error. But a feature that spans ony 1 mil-dot could have up to a 10% error.

It would be a good idea to verify your dot spacing at 16x. A 2.25" feature at 25yds should span exactly 4 mil-dots. If not, adjust the math or magnification accordingly.

If you know that you will be encountering a particular feature on a regular basis (a 7.625" cinder block for instance), and you know that your targets will be within a certain range (10yds to 55yds for FT for instance) you might want to make up a chart for the various dot counts vs distance for that feature. And you can do the same for any other features that you may expect to encounter. Easier/faster than doing the math on the fly.
 
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Here calibrate your optic. :) The attached target is just circles which span a known number of mil dots at 20 yards. Using it you can figure out what the reference magnification is on your optic. Normally the optic has a dot on the reference magnification but not always and even when it does it is not always correct. The reference magnification is the setting where your mil dots line up with the dimensions of the target rings. Once you know the reference you can check your high (and low) magnification to see if it really is whatever the vendor specified it to be.

Ranging is easiest if you use your reference magnification because there is no additional conversion factor. At your reference a mil, is a mil, is a mil.

View attachment 10mils.pdf
 
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OldSpook said:
....

Ranging is easiest if you use your reference magnification because there is no additional conversion factor. At your reference a mil, is a mil, is a mil.
...
Click to expand...
Except that most of us are still using inches and yards. So almost no one does the trig. Instead they use the 3.6"/100yd conversion. I don't think anyone cares that it is the arctan of a milliradian.

When using an inch target to estimate distances in yards, there will always be a conversion factor regardless of magnification.
For SFP mil-dots, the math is the same regardless, but each magnification has it's own factor.

For mil-dots:
At 10X: Distance(yds) = target-size/3.6" x 100yds/dots

At 12X: Distance(yds) = target-size/3.0" x 100yds/dots

At 16X: Distance(yds) = target-size/2.25" x 100yds/dots

At 24X: Distance(yds) = target-size/1.5" x 100yds/dots

At 36X: Distance(yds) = target-size x 100yds/dots


If you want easiest? Use an FFP scope:

For milliradian stadia:
Distance(yds) = target-size/3.6" x 100yds/stadia

For moa stadia:
Distance(yds) = target-size/1.042" x 100yds/stadia
 
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OldSpook said:
Here calibrate your optic. :) The attached target is just circles which span a known number of mil dots at 20 yards. Using it you can figure out what the reference magnification is on your optic. Normally the optic has a dot on the reference magnification but not always and even when it does it is not always correct. The reference magnification is the setting where your mil dots line up with the dimensions of the target rings. Once you know the reference you can check your high (and low) magnification to see if it really is whatever the vendor specified it to be.

Ranging is easiest if you use your reference magnification because there is no additional conversion factor. At your reference a mil, is a mil, is a mil.

View attachment 274105
Click to expand...
Really appreciate it. I know after previously reading awhile ago scotchmo's reply that my Airmax is true on 10x but actuality it's between the 10 and 11. I have my Airmax on my Prosport and usually leave it on 16x because I was sometimes competing in hunter class and can't touch the power setting. But nonetheless thank you for your reply
 
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Scotchmo said:
Except that most of us are still using inches and yards. So almost no one does the trig. Instead they use the 3.6"/100yd conversion. I don't think anyone cares that it is the arctan of a milliradian.

When using an inch target to estimate distances in yards, there will always be a conversion factor regardless of magnification.
For SFP mil-dots, the math is the same regardless, but each magnification has it's own factor.

For mil-dots:
At 10X: Distance(yds) = target-size/3.6" x 100yds/dots

At 12X: Distance(yds) = target-size/3.0" x 100yds/dots

At 16X: Distance(yds) = target-size/2.25" x 100yds/dots

At 24X: Distance(yds) = target-size/1.5" x 100yds/dots

At 36X: Distance(yds) = target-size x 100yds/dots


If you want easiest? Use an FFP scope:

For milliradian stadia:
Distance(yds) = target-size/3.6" x 100yds/stadia

For moa stadia:
Distance(yds) = target-size/1.042" x 100yds/stadia
Click to expand...
Thanks brother now another question. Say you hit 2 mildots low at 45yds. Scope is on 16x but my Airmax has moa 1/4 in turrets. What's the math to make the correction for that?
 
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josh3rd said:
Thanks brother now another question. Say you hit 2 mildots low at 45yds. Scope is on 16x but my Airmax has moa 1/4 in turrets. What's the math to make the correction for that?
Click to expand...
(2 x 2.25") x 4/1.042" = ~17 clicks

If you are going to be doing stuff like that regularly, I would recommend that you get a FFP scope. Either mil/mil or moa/moa.

Note: this discussion belongs in the optics forum
 
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josh3rd said:
Where did the 4 come from?
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I assumed that you meant 1/4 moa turrets.
"...Airmax has moa 1/4 in turrets..."

4 clicks per moa

I don't know what your Airmax actually has, so if you meant 1/4" 100yd turrets:
"...Airmax has moa 1/4 in turrets..."

Then:
(2 x 2.25") x 4 = 18 clicks

1/4" inch turrets are often used on SFP scopes. But rarely on FFP scopes (which are usually moa or mil).

1/4 moa turrets are not exactly the same as 1/4"/100yd turrets. An moa is an angular measurement. A 1/4" is a linear measurement.
 
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Scotchmo said:
Except that most of us are still using inches and yards. So almost no one does the trig. Instead they use the 3.6"/100yd conversion. I don't think anyone cares that it is the arctan of a milliradian.

When using an inch target to estimate distances in yards, there will always be a conversion factor regardless of magnification.
For SFP mil-dots, the math is the same regardless, but each magnification has it's own factor.

For mil-dots:
At 10X: Distance(yds) = target-size/3.6" x 100yds/dots

At 12X: Distance(yds) = target-size/3.0" x 100yds/dots

At 16X: Distance(yds) = target-size/2.25" x 100yds/dots

At 24X: Distance(yds) = target-size/1.5" x 100yds/dots

At 36X: Distance(yds) = target-size x 100yds/dots


If you want easiest? Use an FFP scope:

For milliradian stadia:
Distance(yds) = target-size/3.6" x 100yds/stadia

For moa stadia:
Distance(yds) = target-size/1.042" x 100yds/stadia
Click to expand...
Goodness you are one pretty fart smeller, aren't ya? It's almost like bein' back in school the way you 'splained that. One would think you believed my reply to the OP was directed at you? One would be utterly wrong.

Sure, do it however you want. I was just trying to offer THE OP alternatives. For that matter, what I said STILL WORKS IN IMPERIAL UNITS thank you for showing that a mil is a mil is a mil. That is to say a mil at 100 yards is still a mil at 100 meters. Do the math in whatever units float your boat.

Nobody suggested anyone do the trig. You don't have to do the trig if you simply remember that a mil is one tenth of a meter at 100 meters. Most people STUCK on the imperial system of measurement don't ever figure that out. The rest is straight up proportions to any magnification and any range... all in your head. So for example a sailboat that is ten meters long, which appears in your optic to be one mil wide is 10 kilometers away. Why? Well you see a mil is also a meter at a kilometer or 10 meters at ten kilometers. Yeah, it is a hell of a lot harder than the old imperial system. In a twenty power SFP optic that boat will appear to be half a mil wide... etc. Now let me see, 10km is ... 1.56 kilometers per mile... ayup 10/1.56 = 6.21 miles or there about. Piece of cake. :cautious: But don't make the mistake of assuming I was suggesting the OP do everything in meters... because I was not. To be honest I just didn't think about it one way or another. I was thinking metric and it came out metric. That is all.

As for me, I've done it both ways for nigh on to about fifty years now. There is more than one reason that soldiers do their pace counts in meters.😘
 
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Scotchmo said:
"...Airmax has moa 1/4 in turrets..."

4 clicks per moa
Click to expand...
Except when it ain't... four clicks. But hey, who is nit picking?

If you have not actually checked your optic, you might find out that your 4 clicks are actually 5 or 3 or some number there abouts. Or you might have a 1/10 mil or 1/8 MOA turrets.

I guess if we are going to pick nits we might as well pick all the nits.

Here is a target you can check THAT with:
 
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OldSpook said:
…a mil is one tenth of a meter at 100 meters. …
Click to expand...

And … a mil is one tenth of a yard at 100 yds…

1/10 yd = 3.6”, so that’s what we use in non-metric situations.

It is true that if he keeps his SFP scope at 10x and uses metric measurements, than no conversion factor is needed (just move the decimal point). I’m not trying to discount anyone that does so. I was not trying to cause offense to you or your post. Apologies.
 
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Scotchmo said:
I assumed that you meant 1/4 moa turrets.
"...Airmax has moa 1/4 in turrets..."

4 clicks per moa

I don't know what your Airmax actually has, so if you meant 1/4" 100yd turrets:
"...Airmax has moa 1/4 in turrets..."

Then:
(2 x 2.25") x 4 = 18 clicks

1/4" inch turrets are often used on SFP scopes. But rarely on FFP scopes (which are usually moa or mil).

1/4 moa turrets are not exactly the same as 1/4"/100yd turrets. An moa is an angular measurement. A 1/4" is a linear measurement.
Click to expand...
So that applies at any yardage or just at 100
 
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josh3rd said:
So that applies at any yardage or just at 100
Click to expand...
Yes, Josh, he means that applies to any yardage. He is trying to explain to you that a MIL or a MINUTE are angular measurements. So at 10 yards an MOA is still one MOA but the distance it subtends is 1/10 of what it is at 100 yards. Maybe it would help to watch some of these videos?


An MOA is one minute (1/60) of a degree. There are 60 minutes in a degree. There are 60 seconds in a minute of angle. These angles derive from nautical navigation terms which came about because of the distance the sun appears to move as it traverses the sky in a given time period (a minute, or a second). At a hundred yards a minute of angle is just about 1". At 25 yards it is 1/4 that because 25 yards is 1/4 of 100 yards. At 10 yards a minute of angle is 1/10 of one inch because ten yards is 1/10 of 100 yards. This ratio applies because a minute of angle is a measurement of angle not a measurement of distance.

Have a look at this image:
MOA-Similar-Triangles.jpg

For now suffice it to say this is how it works. It is a bit more complicated than that but for practical field work you can ignore the infinitesimals. =)
 
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