Can someone give a thorough explanation of MOA in relation to scopes?

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brighamr

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What I'm looking for is this:
Say I sight in a scope to be dead on at 100 yards on a .223 rifle. If I need to engage a 150 or 200 yard target, how many "clicks" do I need to adjust for?

Conversly, if I need to engage a 50 yard target.

I kind of understand Minute of Angle, but I don't understand the relation to adjusting a scope on the fly for differing target distances.

TIA
 
If I need to engage a 150 or 200 yard target, how many "clicks" do I need to adjust for?
Click to expand...

Depends on the scope and how much movement that scope gives per click.

Some are more granular than others. Basically you need to know how much MOA change there is per click. 1/4MOA is common.

You will also need to know the bullet drop for your round. If your bullet drops a nice even inch per 100 yards then it's one thing, if it drops 2 inches per 100 yards it would be another. And of course they don't drop in a nice even manner.

If you will look at photos of long distance shooters you'll see a laminated card hanging off the optic. Lots of research goes into making that card :)

Zak Smiths website probably tells how somewhere.

Basically you have to take your rifle, your optic and your ammo and figure it out for yourself or duplicate what someone else has done and hope its close. Depends on how close you need to be.

For something like an industry standard, 5.56 on an M4 for example you can buy scopes with built in BDC (bullet drop compensation). As long as your rifle and ammo meet the standards the BDC is set for you will be pretty close.

If you want the math:

At 100 yards:
Circumference of a circle with a 100 yards radius = 22,620 inches.

There are 360 degrees in a circle so:

One Degree = 22.620/360 = 62.83 inches

There are 60 Minutes in one Degree so:

One Minute = 62.83/60 = 1.047 inches

Luckily for most of us that .047" isn't critical so the 1" per 100 yard rule works well enough. 10.47" at 1000 yards.

That's why the scopes are more granular for some shooters. If you are shooting at 1000 yards a 1/4MOA click moves your point of impact a whopping 2.6 inches. That's waaaay too much for those guys so lots of optics have tighter movement, 1/8MOA or whatever.

Out past, what is it, 1500 yards? It's all way beyond any of my rifles ability (and probably mine too) but somewhere out there you have to begin to take into account the rotation of the earth in your trajectory. That's senior year stuff, I'm still around a sophomore I'm afraid.
 
Texas Rifleman, thank you! I'll have to do some test shots and see about the bullet drop/granularity. I'm shooting an M&P 15 with a weaver 3-9x32 (Click value (moa) minute of angle @100 yds: 1/4 ). It was a scope I bought on another gun but wasn't using much.

Appreciate the info!
 
you need two pieces of info:
dope, generally from a "range card"
number of clicks per minute on your specific scope (read the instructions)

example, if your range card says you need to come up 1.75" at 200 yrds...

if your scope has 1 min clicks, i'd come up one click and expect to be just a smidgen high
if your scope has 1/2 min clicks, i'd come up 2 clicks and expect to be just a smidgen high
if your scope has 1/4 min clicks, i'd come up 4 clicks and expect to be just a smidgen high
if your scope has 1/8th min clicks, i'd come up 7 clicks
 
you need two pieces of info:
dope, generally from a "range card"

Forgive my ignorance, but what's "dope"?

Also, "if your range card says you need to come up 1.75" at 200 yrds..." is the 1.75 difference in bullet drop? or difference in target height?

thanks for the example clicks. I think I'll test it after work. If I have this correct, I can setup a target at 100 and 200 yards. Get sighted in dead center at 100 yards, then check the amount of clicks it takes to get on paper at 200 yards. (targets will be same height).

As long as targets stay relatively the same height, I should then know the approximate number of adjustments between the yardage.... hoepfully :)
 
Say I sight in a scope to be dead on at 100 yards on a .223 rifle
Click to expand...
That right there is your problem!

Zero it at 200 and it will be 1 3/4" or so high at 100, and 8" or so low at 300.

No fiddling & clicking necessary.

Just remember the trajectory figures, estimate the range, and shoot.

rcmodel
 
Forgive my ignorance, but what's "dope"?
Click to expand...

Info...bullet drop at yardage, etc...

Example..

http://www.scopedope.com/

set1.jpg
 
brighamr, my 1.75" example was just something i made up. you need to know what the drop is for YOUR rifle/cartridge. i.e. your dope, i.e. how far the bullet drops vertically at a given range (which is a function of gravity and how long it takes to get there)
 
Out to a certain range, you may not need to change your clicks at all. There is a concept called maximum point blank range.

The above link shows how if one particular .223 rifle is zeroed for 250 yards, the bullet will stay within +- 2 inches of the bore out to 290 yards (less than 250 yards it's over, more than 250 yards it's under). In other words, out to 290 yards, you will hit to within 2 inches of the target (if you do your part) if you just aim at the target and pull the trigger. No click adjustments, no holdover, no holdunder. Pretty slick.

What kind of shooting are you doing?
 
rcmodel - why is zeroing at 200 better?
Click to expand...
For a hunting rifle, you want to extend the "point-blank range" as far as possible.

That is, to get as far as possible to make a killing shot without having to worry about hold-over, scope "clicks" etc.

If you zero a .223 at 100 yards, it's all down hill from there.
100 = Zero
200 = -3" low.
300 = -11" low.
400 = -27" low.

If you zero it at 200, you can hold dead on a coyote from muzzle contact range, all the way out to 300 yards, and expect to kill it.
100 = +1.4" high.
200 = Zero
300 = -7" low.
400 = -21" low.

If you stop do do the scope "clicking thing" the coyote will be over yon hill laughing at you before you get your scope "clicked".

Download Remington Shoot and play with it.
http://www.remington.com/products/ammunition/ballistics/remington_shoot_ballistics_software.asp

rcmodel
 
http://www.eskimo.com/~jbm/calculations/traj/traj.html

or google "ballistic calculator"

you will need your muzzle velocity and the ballistic coefficient of the bullet you're using


edit: however, personally, i much prefer the RSI Shooting Lab software. i think their website is shooting-software.com or shootingsoftware.com or something like that
 
why is zeroing at 200 better
Click to expand...
Because of "Maxium Point Blank Range".

Lets talk deer rifles. If you hit the deer in the heart/lungs it will die, Heart/lungs target is about 10" diameter. That leaves a 5" radius of "error" above and below the target. Average hunting rifle percision ~1.5 MOA, which is ~4" @ 240 yds. This leaves a 6" window to still kill (3" above, and 3" below @ 240 yds)

If the deer is at 15 yards with a 200 yd zero you will be 1" low, and still kill.

If the deer is @ 100 yds with a 200 yd zero you can aim right at the center of the kill area, be 2" high and still kill.

If the deer is @ 200 yds no problem.

If the deer is @ 240 yds you will be 2" low and still kill no problem.

The rifle has a MPBR of ~240 yds, just aim in the center from 0-240 yards and you should kill.

If the deer is @ 350 yards you need to either hold over or change scope. Because we dont "change the scope" while deer hunting you either learn hold over, or you get closer. I recomend just getting closer.

Last but not least you should remember how well you shoot(not the rifle). Find out how far YOU can hit a 5" radius circle with a real hunting type rifle and rest(not a sandbaged bench rest), it is usually under 300 yds.
 
Some people have an aversion to turning the elevation knob. And you don't need to, if you're hunting animals with a 12" kill zone at 300 or less. Do a search on the JBM ballistic calculator. You can enter your specific bullet, and print a range card, out to 1000, or whatever you choose. Then if you have 1/4" clicks and are zero'd at 100, 1 click at 200 is 1/2", at 300 it's 3/4", at 400 it's 1", etc. So if your range card (dope) shows you need to come up 6" at 500 yards, you know that 1 click is 5/4" at 500 yards (1/4 * 5). So to come up 6" you would use 4.8 clicks, which you round to 5.

I may have misunderstood, if you're just hunting, do what the previous guys said.
 
"Download Remington Shoot and play with it.
http://www.remington.com/products/am...s_software.asp

rcmodel"

From Remingtons site: System Requirements: Windows 95, 98, NT or 2000 LOL

I think I have win95 floppies around somewhere :D

I'm checking the other sites though, and think I'm understanding things a bit better.

Thanks to all for the ideas and information, this is one area I really lack knowledge in.
 
brighamr, it doesn't matter how high or low your target is. I'm assuming you'd still be aiming at the center of the target. It just matters how far your round will drop. If your round drops 6 inches at 300 yards with a 200 yard zero, then when shooting at 300 yards you need to either (1) aim six inches high (which can be hard to figure out through your scope) or (2) change the scope to aim six inches high and then you put the reticle back in the center of the target. If you are buying factory ammo, you can look at the back of the box and it will tell you how far the round will drop (although these are averages, and performance in your rifle may vary). Or, you can google any of the ballistic calculators. Federal even makes one available as a down loadable application for all of their ammo.
 
Tx1911 - what I meant by target height was uphill/downhill shooting. (I know there's some differences/tricks there).

As for the 200 yard zero, I'm convinced that's a good idea.

All the sites/links have really helped. I'm going to read through them, then after work test some of the ideas (little knowledge overload right now :D )

Thanks again everybody
 
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