lost on come up in MOA and my scope

[UT PROSIM]

i just printed off a ballistics chart for my 308 and it has come up in MOA as one of the rows on the chart. i have a 1 click = 1/8" at 100yd turrets on my scope so how do i apply that to this chart. i think i am really over thinking this. for example at 400 yards there is 7.4 MOA come up does that mean i adjust to 300 yards then add on 7.4 MOA of adjustment? 7.4 MOA at 400 yards is 29.6" but the trajectory given is -31"
any help would be great

 

[dmazur]

A MOA is an angular measurement, which subtends 1.047" at 100 yds. (For rough calculations, many round this to 1", but it really isn't exactly one inch.)

7.4 MOA isn't 29.6" at 400 yds, but is 30.99" (which someone rounded to 31".)

My understanding of this is that you need to adjust for 31" of hold over (or "come up") to have POI = POA at 400 yds. Since your scope clicks in 1/8" increments at 100 yds, it would be -

(100 yds / 400 yds) x hold over of 31" = 7.75" hold over at 100 yds
7.75" / 0.125" per click = 62 clicks.

Another way to do this is to convert the scope click size based on actual range -

1/8" click at 100 yds is 1/2" at 400 yds.
31" hold over / 0.500" per click = 62 clicks.

I think it's a lot easier if you don't bring MOA into things, but just work in inches of drop. A lot of folks (me included) get tangled up in thinking MOA is some kind of linear measurement instead of an angular measurement...

 

[nastynatesfish]

Try this site for a balistic calculator. I took my 7mm out and used it great out to 800yrd at 6" steel plates. That's plenty accuate for me for now.
biggameinfo.com

 

[benzy2]

As said, MOA isn't exactly 1" at 100 yards and as such, as the distances increase, the difference between the two becomes apparent.

If your scope really is 1/8" per click at 100 yards that adjustment will change proportionality with changes in range. At 200 yards it will move impact by 1/4", 400 yards will be 1/2", 50 yards will be 1/16" and so on. So for 31" at 400 yards, you need 62 clicks.

Those numbers of elevation (both MOA and inches) are from a given zero, I'm guessing 100 yards but don't know. What you do is zero the rifle at whatever the specified distance is on the ballistics chart and then from there you adjust whatever the number of clicks would be. So if it says to zero at 100 yards, then if you go to 200 yards and you need say 10 clicks of elevation and then at 300 you need 25 clicks, both would be relative to the 100 yard zero. So if you zero at 100, add 10 clicks to get to 200, then decide to move to 300, you would only add an additional 15 clicks to give you a total of 25 clicks from your 100 yard zero. (These values are made up for simplicity of the example, but would just be replaced by whatever your ballistics chart states).

 

[LRS_Ranger]

1/8th MOA? That's a lot of clickin! Anyway, here's a good way to do it. I assume that you can reset your turrets to zero once you are on the x at 100. Once you do that, make an entry in your dope book at 100 as 0+0. If memory serves, my 300 meter is 4.25 MOA up, which I would enter as 0+4.25, meaning 0 full revolutions and 4.25 MOA up, above zero. If I had to dial in 25 moa, I would enter 1+10, because my scope has 15 MOA per revolution.

To me, this is easier than doing addition and subtraction on the fly while I am trying to hit a target. If you know the range, just crank it to the known position and send it.

 

[LRS_Ranger]

I read your origional post too fast and didn't really answer your question I don't think. Here's another try. The numbers that the printout has are the come-ups for a 100 yard zero. The way it is written, to find your adjustment going from 300-400 you would have to subtract the 300 from the 400 value. That would tell you how many additional clicks. The reason that your MOA and inches calculations are slightly off is that 1MOA is 1.04 inches at 100, or something like that. That is the reason that the math is slightly off. Hopefully that was more on target with your origional question.

 

[rcmodel]

Or, you could just sight it in for maximum point blank range and learn hold-over.

Say you sight it in 1.25" high at 100 yards.
It will then be very nearly zeroed at 200, 9" low at 300, and 25" low at 400.

Thats MOD (Minute Of Deer) as far as you can accurately estimate range to the deer without a range finder.

rc