Rifle Scopes ranging with mil dot based on zoom?

[llajumpvid]

Am I doing this correctly?

I have a 4-16 power mil dot Mueller scope. 8x is the power that the mil is sized for. I want to use the zoom to estimate distance for an 18" object.

So at 8x an 18" object will read 1 mil at 500yds
1.047*5=5.235"=1MOA
18/5.235"=3.438moa

If scope at 6x 8/6=1.333
500/1.33=375yd
@375yd 18" is 18/(1.047*3.75)=4.58moa
4.58/1.333=3.438moa=1 mil
375/6=62.5

If scope at 10x 8/10=0.8
500/0.8=625yd
@625yd 18" is 18//(1.047*6.25)=2.75moa
2.75moa/.8=3.438moa=1mil
625/10=62.5

So If I zoom an 18" object to fit into 1 mil spacing and read the magnification multiply by 62.5 (60 for simple math) I would get the approximate distance? e.g. I zoom in on an 18" object to fill 1 mil and read a zoom of 6.4 6.4*60=384yd...really 400 but should get me within an inch or two

 

[Lindy]

Re: ranging with mil dot based on zoom?

If you're trying to get maximum accuracy for ranging, I think the best way to do that would be to measure the object at the maximum power of the scope, for maximum accuracy in reading the size of the object in mils.

Then use your Mildot Master or the mil relation formula to calculate the range. Since the object at 16 power will measure twice what it will at 8 power, you will then need to multiply the resulting range by two.

 

[Lindy]

Re: ranging with mil dot based on zoom?

P.S. - to ensure that your powers are correct, you might want to check the calibration of your power ring.

See:

Optically Checking Rifle Scopes

 

[llajumpvid]

Re: ranging with mil dot based on zoom?

Agree completely but was hoping the concept was correct so that in a pinch I could use it. The math is simple enough to do in my head.

 

[Lindy]

Re: ranging with mil dot based on zoom?

Having a target which is an even fraction of a mil may make the task seem easier. If the target is not - say 22 inches - it may be harder. I try to avoid mental math in situations where there is time stress.

 

[kombar]

Re: ranging with mil dot based on zoom?

It would be easy enough to just make an excel spreadsheet of some different target sizes and the constants you would need to multiply by to get the range.

Really, all you'd have to do is multiply 1000/36 by your target size in inches and divide by 8 to get the constant for that particular target size.

So, in Lindy's example, the constant for a 22 inch target would be 1000/36*22(inches)/8, or 76.4. If the reticle was calibrated for some value other than 8x, just sub it in the formula.

 

[llajumpvid]

Re: ranging with mil dot based on zoom?

I have a nice spreadsheet that I have on my phone that works great. Just in the field it's difficult to take my attention off the target to enter the data...plus in sunlight the screen on the phone sucks. Just thought for a quick estimate the zoom method would get me within 2"+/- for computing bullet drop. I'm not looking for ranging this way beyond about 400yds.
I have the spreadsheet set up to compute distance off the mil reading and calculate wind and bullet drop (plus lead) where you enter wind speed, direction and target speed. It will also let you input a known distance to compute the same. I have separate tabs for different ammo. Right now I just copy and paste the ballistics data from http://www.biggameinfo.com/BalCalc.aspx and the spreadsheet calculates off of it.