Difference between 1/4" or 1/4 MOA clicks?

[Song Dogger]

My Leica Geovid HD-B Edition 2200 range-finding binoculars provide "hold" values in 1/4 MOA clicks. My Swarovski Z5 3.5-18x44 scope has 1/4" clicks for 100 yards. Knowing 1 MOA is 1.047" at 100 yards, the difference between 1/4 MOA or 1/4" clicks seems insignificant. To prove that, everyone points to the fact that 1 MOA at 1000 yards is 10.47", a mere 0.47" off the 1" per 100 yard rule-of-thumb estimate. So, let's say the Geovid suggests 84 clicks at 900 yards. Using their 1/4 MOA, that's a hold of 198" (84 x 1/4 x 9 x 1.047"). Using Swarovski's 1/4" at 100 yards, that's a hold of 189" (84 x 1/4 x 9 x 1"). So, if both products are dead on, I'll shoot 9" low at 900 yards. That's 1 MOA of error! That can't be right, can it?! What am I doing wrong?

 

[WeiserBucks]

The equation multiplies as distance increases. It's angular, not linear.

 

[Canhunter35]

Thats so strange that your swaro scope tracks in inches. I've never heard of that before

 

[Wedgy]

I looked on several sites including Swarovski's and they all say 1/4" @ 100 yards, I have only seen this on my cheap rimfire scopes.

 

[Canhunter35]

I looked on several sites including Swarovski's and they all say 1/4" @ 100 yards, I have only seen this on my cheap rimfire scopes.

That's mighty convenient.

Your calculations of Moa and inches it will drop is correct. I'm not sure but 9" difference may be correct

 

[Song Dogger]

Hmmm. Looking further, both Swarovski's website and my scope say 1/4" or 7mm per click at 100 yds. 1/4" = 0.250", 7mm = .276", and 1 MOA = 0.262" (1.047/4). All close enough for sighting in at 100 yds, but the differences seem significant at a couple hundred inches of drop.

 

[FearNoWind]

1 MOA at 100 yards is always 1 MOA. 1 MOA at 1000 yards is always 1 MOA. If you interpret 1 as 1inch then 1 MOA will be 1 inch. If you interpret it as 1.047 then it will be 1.047 inches. Because MOA is an angular measurement (1/60th of a degree) it represents a constant linear calculation over distance. 1 MOA is always 1 MOA. The place where some get confused is that, as an angular measurement, its linear component means 1 MOA at 100 yards is 1 inch (we round it to 1 inch for sake of simplicity) 8 inches at 800 yards and so on.MOA x distance in yards = point of aim. Because the bullet travels in an arc, the amount of correction necessary to connect with a target over distance is not linear it is exponential. In a ballistics environment, in order to produce an accurate "dope" (data on previous engagements) sheet, any initial assumption must be compared with actual test results.
Any time you have two instruments making different recommendations regarding a firing solution there is either something different in the raw data entered or the instruments have been programmed with inconsistent default assumptions.

 

[kyron]

that's a hold of 198" (84 x 1/4 x 9 x 1.047"). Using Swarovski's 1/4" at 100 yards, that's a hold of 189" (84 x 1/4 x 9 x 1"). So, if both products are dead on, I'll shoot 9" low at 900 yards.

well, yeah 198" minus 189" is a 9" difference

 

[Song Dogger]

First, I was wrong in that Swarovski's turrets are either ¼" or 7mm in 100 yds. It's 7mm in 100m, which is essentially equivalent to ¼" @ 100 yds. Duh. Still, the lessons in math, trig, and simple ballistic concepts are unnecessary. Guess what I really need are better writing skills, because I don't have two instruments suggesting differing firing solutions. It's about two different ways to measure the same firing solution – clicks using ¼" @ 100 yds versus ¼ MOA (I did not put a distance on the 1/4 MOA because I realize 1 MOA is 1 MOA at 100 or 1000 yds!).


Mostly, I was looking for verification on how to calculate clicks from hold since I couldn't find an online solution to chart that. I think I got that verification, though, especially since the formula I used could accurately predict the Geovid's readings in "clicks" from "hold" on the same target. I was also expressing some surprise at the difference between click values at longer distances using 1/4" @ 100 yds versus 1/4 MOA turrets.


All this stemmed from comparing the Geovid firing solutions to a ballistics chart, which I wanted to validate before heading to the range for testing. That's the best point made, by the way, that actual test results are the "final answer" – not just for the Geovid, but to validate Swarovski's reputation for click repeatability/consistency, which is more important than ¼" @ 100 yds versus ¼ MOA. I'm ready to do that now, so let the fun begin!

 

[7magcreedmoor]

Ah, the old "rounding error" problem. Calling 1 MOA an inch at a hundred yards is okay for the first couple hundred yards. Take 400 yards for example: from a 100 yard zero your dope might call for 5.8 MOA up, which is 24.29 inches using true MOA but 23.2 inches using rounded off MOA. Hitting within 1 inch of your point of aim at 400 will make most of us quite happy, especially if there are witnesses. But rounding it off will start to cause problems if you shoot far enough. 10 inches compared to 10.47 inches is the difference between one "actual" MOA and one "shooter's" MOA at 1000 yards. Doesn't seem like a big deal, does it? A typical "high power" centerfire load might require 25 MOA dial up from a 100 yard zero to hit a 1000 yard target. Now we will have an issue, as 25 times the 0.47 inch discrepancy will have us hitting a foot high or low depending on which of your tools was using the rounded off figure. The error won't be as apparent in windage, as a 10mph wind correction at 1000 will likely be somewhere between 5 MOA depending on the BC of the load, so 5 times that 0.47" error and you hit plus/minus 2.5 inches from where you'd hoped. You would likely write that off to a "bad wind call" and go on about your business.

 

[Song Dogger]

On point, sir! I have the customizable ballistic turret on my Swarovski scope, which only has 53 clicks of elevation adjustment. It's meant for hunting more than tactical/target situations. Well, 53 clicks on my rifle is right at 700 yards, where the rounding error you discuss is 5". A little worrisome, but I've yet to shoot beyond 500 yards in a hunting situation, where the error is closer to 2 1/2". So, pending range test results, my current set-up is probably good to go. If I decide to upgrade scopes for longer distances, though, I now know to look for click calibrations that'll match the Geovid's.

 

[Canhunter35]

At 700, using an incorrect density altitude will cause more elevation differential than 2.5"

 

[Song Dogger]

Assume the point you're making is that there are factors that can affect shots more than "rounding error". If so, agreed. That's why I'm trialing the range-finding Geovid binocs - it has real time temperature and air pressure sensors and uses them in its ballistic calcs.

 

[Canhunter35]

Yes that's what I meant. Sorry for not clarifying