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MOA Ranging Formula

 
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  #1  
Old 05-06-2014, 08:41 PM
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Join Date: Apr 2013
Location: west central Indiana
Posts: 36
MOA Ranging Formula

Started messing around with this formula using my Vortex Viper HS-T set on 16 power. Target is 36in. tall set at 800yrds. Target is 4 MOA looking through scope. Formula is heigth of target x 95.5 MOA = yards. The yardage was shot in with my rangefinder. Equation, 36 x 95.5 4 = 859.5 tell me what is wrong here. 60 yards is another 10 clicks for me and that is a little over 20in. drop. That my friend equals a clean miss. So is my rangefinder off or or the MOA on the scope or what. Just want a good way to a estimate yardage if the electronics fail. Thanks.
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  #2  
Old 05-06-2014, 09:00 PM
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Join Date: May 2012
Location: Lebanon County PA
Posts: 167
Re: MOA Ranging Formula

I have not handled the HST, but have both the SFP and FFP HSLRs, and have found the reticle patterns in both to be very close to spec when measured against a test target I created set at 100 yards (laser confirmed). If your rangefinder is on and that 800 yards is a good number, and your mag setting was tight on 16x, then is it possible that your rifle wasn't quite solid enough to get a good visual? 800 yards is pushing it for reticle ranging accuracy even with very high end resolution, and the math indicates that IF the visual measurement had been 4.29 MOA ( kinda hard to discriminate 4 from 4.29 when the hash marks are 2 MOA apart), that would have given you your 800 yards. Parallax can also mess you up as your eye looks away from optical center when trying to bracket the target. The longer the distance, the more the variables start to pile up against you- Long Live the Laser!
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  #3  
Old 05-06-2014, 09:51 PM
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Join Date: Apr 2013
Location: west central Indiana
Posts: 36
Re: MOA Ranging Formula

Thank you very much for the reply. So at what yardages do you think the formula can be accurately used to, without to many variables comment I to play.
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  #4  
Old 05-07-2014, 04:13 PM
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Join Date: Oct 2005
Location: Great Falls, MT
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Re: MOA Ranging Formula

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.
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  #5  
Old 05-07-2014, 04:17 PM
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Join Date: Apr 2009
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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.
Very valid point made here. The HS-T is SFP.
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  #6  
Old 05-07-2014, 07:18 PM
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Join Date: May 2012
Location: Lebanon County PA
Posts: 167
Re: MOA Ranging Formula

There are a pile of factors that affect the accuracy of reticle ranging. I looked at your reticle on Vortex's website, and one of the limiting factors is the 2moa interval of your grid. The thin lines are 0.15 moa wide, but you don't have anything definitive in between those two measurements. Judging one moa is do-able pretty easily, but for most trajectories that interval is too coarse for ranges 500 yards. At my club we have steel targets of various shapes at each berm, from 200 to 500 and the farthest is 640 (behind the competition target pit). For practice, I make my most careful measurement of each plate, then when I go to paint them I'll get out the tape and see how close I was able to come to the truth. It is a humbling exercise. My HSLR has both 1moa and 0.5moa hashes, which improve my chances. Your tactical reticle is intended for quick ranging of man-size targets, which are taller kill zones than most game animals, hence more forgiving. You said in your OP that the target is 36 inches tall- if there was any angle aspect to your line of sight, this may have skewed your measurement, like when looking up or downhill at a deer makes the body look smaller, leading to an over-estimation of range. When scoping a target of known dimension, you must account for any perspective angle and use the least distorted dimension. And one more note on FFP: the one I use has an open center cross with a 0.15moa dot. A target has to be pretty small to be obscured by that.
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  #7  
Old 05-07-2014, 09:13 PM
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Join Date: Apr 2013
Location: west central Indiana
Posts: 36
Re: MOA Ranging Formula

Thank you all for your input. 7mag, you are a professor. Thanks Again, Greg
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