Aeon 8-32x50 true mil dot?

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For a standard SFP mil-dot scope, the magnification where mil-dots are milliradfians is 10x. But scope markings are rarely exact. And some manufactures use settings other than the standard 10x magnification.

If you want exact milliradians for some reason, set as ruler or yardstick out at 27.78 yards (83'+4"). Adjust the scope magnification until each mil-dot lines up on an inch mark.

Use that magnification when you want milliradian dot spacing.

 
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A milliradian is distance/1000.

Dot spacing in inches = (distance to target in inches/1000)

or as Tvanpool said:

(distance to target in yds, /100)*3.6

or:

(distance to target yds)/27.78

For a standard SFP scope, those formulas apply at 10x only.

The formula for any magnification is:

Dot spacing in inches = (distance to target in inches)/(magnification x 100)

or:

(distance to target in yards) x 36/(magnification x 100)

Remember that the markings on the magnification ring are not always accurate.
 
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I used to think that the best way to "measure" subtension was to rangefind different size targets at different ranges and leave the subtension variable in the mil-ranging equation as the variable, calculating it for each "sample," then take an avg. for each set. I haven't proven this yet, but it seems like that would be very accurate assuming you have enough samples to make for good accuracy.
 
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"sscoyote"I used to think that the best way to "measure" subtension was to rangefind different size targets at different ranges and leave the subtension variable in the mil-ranging equation as the variable, calculating it for each "sample," then take an avg. for each set. I haven't proven this yet, but it seems like that would be very accurate assuming you have enough samples to make for good accuracy.
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The subtension can be a variable, even at a single "magnification setting". At least for close targets.

So I take one precise spacing measurement at each incremental distances. And I don't average it out.

Reticle spacing is not always linear when focused on close targets.

The factor can vary a significant amount as you get inside 20 yards. Not so much at 20+ yards. 5-10% variation between 10 yards and 55 yards is not uncommon. I end up using a unique multiplier for each distance, even when the magnification setting stays constant.

Example of one of my scopes:

1) Set scope to max magnification (12x for this scope).

2) Set a yardstick at exactly 10 yards. Focus precisely. Count how many inches will span 10 mil-dots. It reads 2.94".

3) Set a yardstick at exactly 30 yards. Focus precisely. Count how many inches will span 10 mil-dots. I should get 3 x 2.94 = 8.82". But I actually get 9.43".

Conclusion: Even when a dot spans 0.9" at 30 yards, that does not mean it will span exactly 0.3" at 10 yards.
 
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