Scope Adjustment Question

[possum]

i know you guys can help. be advised i have no experience shooting at anything past 300 meters. this has to do with using a scoped bolt rifle.

say i have a rifle .308 zeroed at 100yds.

also say that i want to shoot at a target at 200yds with a 100yd zero and the bullet is gonna drop 2" (just to keep it simple)

that would be 2 moa right?

also say that my scope has 1/4moa adjustments.

now say that i want to adjust the scope. i would have to do 16 clicks right?

4 turns equals an inch at 100yds, 8 turns would equal 1 inch a 200yds, so therefore i would need 16 clicks to give me 2" at 200yds?

i have been at this all day looking and trying to figure this stuff out, about come ups and trying to learn the mil dot system to no avail.
i know you guys will square me away! thanks

 

[Flyrodder]

Under 100yds, you adjust more clicks. Over 100yds, you adjust with less clicks. 4 clicks would move the bullet 2 inches at 200yds. flyrodder

 

[Zak Smith]

1 MOA = 1.0472 inches PER 100 yards.

 

[USSR]

possum,

For the sake of making this easier to comprehend, we will say 1MOA = 1" at 100 yards, although it is actual 1.0472" as Zak said. Here is the way it works:

1MOA = 1" at 100 yards
1MOA = 2" at 200 yards
1MOA = 3" at 300 yards, etc.

So, if you're zeroed at 100 yards and your bullet is dropping 2" at 200 yards, then you need to correct by dialing in 1MOA of "up" (4 clicks with 1/4MOA adjustments) to zero at 200 yards. Hope that helps.

Don

 

[taliv]

possum, i think you're off a bit there.

like zak's formula,
1 MOA = 1" @ 100 yrds, 2" @ 200 yrds, 3" @ 300 yrds, etc

assuming you're talking about a 308win, and it's zeroed at 100 yrds, then at 200 yrds, it will drop about 4", which at 200 yrds is 2 MOA.

that means you'll turn your knob 8 clicks

and it's the equivalent of .6 MILs, which I'd recommend ignoring till you get the MOA system figured out. Even so, if you have a MIL reticle in your scope, then you'd hold over .6 MIL in order to hit the target at 200 yrds.

in your example, where you've guessed it would drop 2", that would actually be only 1 MOA @ 200 yrds, in which case, you'd only turn the knob 4 clicks.

 

[Zak Smith]

Don't think in terms of "clicks", or in terms of "incremental inches" (ie, 4" from 100 to 200). Think in terms of total correction from your primary zero (eg 100 yards) to the actual distance; then dial it directly on the scope. Don't count clicks. It has numbers printed on the knob for a reason.

 

[possum]

thanks to all. i appreciate it, so the moa stays constant all the time. ie

if you are needing to come up 2 moa at 200yds then 8 clicks.

4 moa at 300yds 16 clicks,

alright i am gettig it now. thanks gentelmen.

 

[Art Eatman]

Some FWIW:

If you zero for 200 yards by shooting two inches high at 100, you'll be roughly six inches low at 300. You'll be about two feet low at 400, and some four feet low at 500. ("round numbers" for a .308 and 150-grain bullets)

If you have a rangefinder and a quality scope, you can adjust the scope. For me, generally, while hunting, I've guesstimated the range and used Kentucky windage for holdover. So far, so good...

 

[Nate C.]

Why not zero the rifle at 200?

 

[Zak Smith]

article | Practical Long-Range Rifle Shooting, Part III - Shooting

Zeroing simply means to set the point of impact at the point of aim at a certain distance. This distance, called the "primary zero", is the where the bullet will impact where the cross-hairs are pointed, when the elevation and windage knobs are zeroed out and have no adjustments applied.

I recommend using a 100-yard zero instead of a longer-distance zero for several reasons. First, any wind that is present will have a very small affect on the zero. Second, if you are "off" in distance by up to 10 or 15 yards, the effect on your zero will be minimal. For example, if you're actually shooting at 90 yards or 110 yards instead of 100 yards exactly, the difference in point of impact will be less than a tenth of a minute. Lastly, 100 yards is so short a distance that if you travel up or down in altitude, or if the temperature changes dramatically, your primary zero will not be affected. Longer-distance zeros such as 500 yards will become invalid with large environmental changes such as those, because the air density will affect the point of impact. When running a 100-yard zero, the primary zero stays valid, and you just need to adjust your down-range dialed trajectory.

If you're going to dial elevation to compensate for drop at longer ranges, you gain nothing with a 200 yard zero over a 100-yard zero. Besides the things mentioned above, now to be spot-on at 100, you need to dial "down", which is needless and more error prone. Want a 200-yard zero as default for the field? Just dial up 0.4-0.5 mils (or 1.75 MOA for those of you stuck in MOA). You have a knob-- use it.

 

[possum]

zak,
once again thank you and i will be going with the 100yd zero i figured on doing this before reading your post but that gives all the reasons to sick with the 100yd zero thanks.

 

[rangerruck]

that is another thing, as Zak mentioned, make your corrections from your zero, don't think of you/rifle as the starting point. And then again, once you start getting past 300 yds, other atmospheric conditions start coming into play, plus your bullet drop starts to happen at a more rapid pace.

 

[jmr40]

While most of the responses are correct I think there is a simpler way to explain it. At least it is easier for me to undrstand. Most scopes move the point of impact 1/4" for each click at 100 yards. That would mean 1 click equals

1/8" at 50 yards
1/4" at 100 yards
1/2" at 200 yards
1" at 400 yards.

 

[CB900F]

Jmr40;

You beat me to it, you rascal you.

900F

 

[rangerruck]

that is totally right, but remember, after 300yds, you really need to compensate for atmospheric conditions, and also the rapidly changing speed , and trajectory.
In other words, even if your atmospheric conditions were perfect, your bullet is going to start dropping more rapidly, so you cannot just use an even number of clicks like that, you need a chart to show you how much your drop is going to be based on speed and weight of projectile , leaving your muzzle.
Unless you allready have shot your weapon enough to know how much it drops at 300 , 500 , 800 yds, etc., based on your 100 yds zero.