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MOA Ranging Formula

 
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  #8  
Old 05-10-2014, 04:33 PM
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Join Date: Mar 2014
Location: West Texas
Posts: 278
Re: MOA Ranging Formula

Quote:
Originally Posted by MT4XFore View Post
Is your scope a first or second focal plane? Is 16 the highest power? If it isn't a first focal plane scope, it must be set to it's highest power for the reticle calibrations to be accurate. Hope this helps.

Unless your scope is the new HS-T 6-24x50 in which case the reticle is only accurate at 18 power (I have no idea why they did this. It came as a surprise to me). There is actually a detent at 18 power to help you feel it without looking at the marks.
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  #9  
Old 05-10-2014, 08:34 PM
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Join Date: Apr 2013
Location: west central Indiana
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Re: MOA Ranging Formula

Mine is the 4x16 HS-T and all estimates are made on 16x.
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  #10  
Old 05-11-2014, 08:17 PM
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Join Date: Feb 2003
Location: Pueblo, CO
Posts: 1,182
Re: MOA Ranging Formula

Here's what I assume the reticle looks like-- "E". Even the thickness of the lines can throw your estimation/calcs off somewhat. Darrell Holland and I have a theory about interpolating between stadia lines of reticles for rangefinding purposes in that people tend to guess between the edges of the stadia lines and not from the center of the line to the center of the next line. That throws the interpolation off (a lot at that distance) and now the subtension should probably be 4 MOA-.15 or 3.85. Now the equation becomes 36 x 100 / 1.0472/3.85 = 892 yds.
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  #11  
Old 05-11-2014, 10:44 PM
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Join Date: Feb 2003
Location: Pueblo, CO
Posts: 1,182
Re: MOA Ranging Formula

What you may want to do with that reticle is to range a bunch of targets at different distances and then recalculate the actual subtension (the 2 MOA units) from those readings, i.e. say a 10" target at 223 yds. occupies 2.3 2 MOA units, then the equation becomes--

10 x 100 / X / 2.3 = 223

X=1.95 inches @ 100 yds.

...now do 10 more or so and "reverse-mil" (as above) the subtension, average it and just use that as your "useable" subtension factor in the equation.

I have found that most reticle-ranging falls apart beyond 500-700 yds. or so depending mostly on size of target relative to subtension unit, magnification, and resolvability.

Last edited by sscoyote; 05-11-2014 at 11:48 PM.
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  #12  
Old 05-12-2014, 06:24 PM
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Join Date: Feb 2003
Location: Pueblo, CO
Posts: 1,182
Re: MOA Ranging Formula

Quote:
Originally Posted by mountainman56 View Post
Unless your scope is the new HS-T 6-24x50 in which case the reticle is only accurate at 18 power (I have no idea why they did this. It came as a surprise to me). There is actually a detent at 18 power to help you feel it without looking at the marks.

MM, I actually prefer a mil-dot reticle that's not set up for the highest power in a 2FP scope. This way I can apply it at the highest power to achieve a smaller subtension for more accurate windage and rangefinding applications. This is a 6-18X Nikon Buckmaster I set up on a 17 Fireball XP-100. The mil is set up for 12X, but I apply it at 18X where it becomes 12/18x3.6=2.4 IPHY. Great for windage reference and rangefinding. This little rig has had some 1st shots to right around 500 yds. using the lowly 25 Hornady HP in some wind occasionally--

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  #13  
Old 05-13-2014, 11:32 AM
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Join Date: Jan 2012
Location: Houston, Texas
Posts: 1,042
Re: MOA Ranging Formula

I use the formula
(( target in inches ) \ MOA ) x 100 = distance

I.E.
36/4 x 100 = 800

This is simple enough that most of the time i can do it in my head.
Often i estimate the largest the target could be, then the smallest it could be and average the two together for my target distance. ( This helps in mirage )

Then i range the target and see if my estimation was close enough to yeild a hit. I do this before every shot in practice.

Every so often me and a friend will go do a cold bore contest where we walk to different ranges and leave the rangefinders in the truck.

6-7 hundred is my max for mil-ing a target.
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  #14  
Old 05-13-2014, 05:42 PM
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Join Date: May 2012
Location: Lebanon County PA
Posts: 310
Re: MOA Ranging Formula

When using quick math to calculate in your head, beyond a certain range you need to start correcting for the rounding off error- the flatter your load shoots, the farther out you can get by with quick calc, but the round off will get you eventually. After doing the quick math (30in target divided by 6MOA times 100 equals 500 yards) you need to subtract 4.5% to get rid of the rounded off MOA. The 22.5 yard difference can cost you the shot that far out, maybe even closer depending on your load. Or you can use 95.5 instead of 100 if you have a calculator, or are much more confident with your mental math than I can ever be...

I cheat and lop off 5yds per hundred if I have no calculator. Still a little round off, but can get a bit farther out before it gets me.
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