Scope moa


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N1YDP
March 20, 2013, 11:09 AM
can anyone explain moa in easy terms. i found this chart.i have a 1/8 moa scope, if i was shooting 1 inch low at 400 yards by the chart would it be 2 clicks?

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hey_poolboy
March 20, 2013, 11:31 AM
Without getting into all of the math (fun) an moa equals about 1.04".
So, at 100 yards your 1/8 moa clicks equal aprox. 1/8". At 200 yards they should move your poi (point of impact) about 1/4" and at 400 yards it will move you aprox. 1/2".

Sent from my DROID RAZR using Tapatalk 2

N1YDP
March 20, 2013, 11:47 AM
show me the math.i am not a math wiz,but i will try to understand it.

SlamFire1
March 20, 2013, 12:05 PM
1 MOA equals 1 inch at 100 yards. 1/2 MOA equals 1/2 inch. 1/4 MOA equals 1/4", 1/8 MOA equals 1/8"

1 MOA equals 2 inches at 200 yards. 1/2 MOA equals 1 inch. 1/4 MOA equals 1/2", 1/8 MOA equals 1/4"

1 MOA equals 3 inches at 300 yards. 1/2 MOA equals 1 1/2 inch, 1/4 MOA equals 3/4 inch, 1/8 MOA equals 3/8"

1 MOA equals 4 inches at 400 yards. 1/2 MOA equals 2 inches, 1/4 MOA equals 1 inch. 1/8 MOA equals 1/2 inch

Therefore if you are one inch low at 400 yards, and how anyone can hold that tight at that distance I don't know, then two 1/8 MOA clicks (1/2" plus 1/2") will raise the group up one inch.

More or less.

N1YDP
March 20, 2013, 12:17 PM
so i guess i am reading that chart right.i am getting into benchrest shooting,so i would like to learn the math for 1 moa = 1.047.
say i am zero at 100 yards and i want to be zeroed a 200 yards,what would the math look like using 1 moa=1.047.

taliv
March 20, 2013, 12:34 PM
n1ydp,

there are 360* in a circle

a "minute" just means 1/60th of something just like a 'percent' is latin for 1/100th of something

so one "minute of angle" really means one "minute of a degree", or in other words, 1/60th of a degree.

basic trig formulas (you remember sin, cos, tangent...) allow you to calculate any one of these three things, if you know the other two:
distance to target
height of target
angle

e.g. if you wanted to come up 1" at 400 yards, you know 2 of those three things and the third is the angle. (MOA is an angular unit of measure)

for expediency, some people use "Shooter's MOA" SMOA or IPHY "inch per hundred yards" because it's close enough (meaning, their guns aren't accurate enough for them to tell the difference between 1" per 100 yards and the more exact precise measurement.

using IPHY, 1 MOA at 400 yards is 4" and if you're looking for 1" that would mean you need to come up 1/4 MOA. Since your scope turret is in 1/8th MOA increments, then you need 2 clicks.

that make sense?

hey_poolboy
March 20, 2013, 12:39 PM
Here's a link (http://www.snipercountry.com/articles/mildot_moa.asp)to a decent article by Jay Williams on the subject.

If you google it there are many more.

taliv
March 20, 2013, 12:44 PM
although, actually, most people calculate it a different way....

imagine yourself standing in the center of a circle. imagine the target is on the circle. that makes the distance between you and the target = the radius of the circle.

now if the radius is 400 yards, you can use forumula 2 x radius x pi to get the circumference. in this case, 2513.2 yards

now convert that to inches by multiplying by 36, gives you 90475.2 inches. now, divide by 360* means each degree in the circle subtends 251.32 inches. now divide by 60 to get minutes. each minute is 4.188 inches. (as compared to 4" even using IPHY)

so 1/8th of a minute is .5236 inches at 400 yards.

that means every time you click your scope you should theoretically be moving the bullet impact roughly half an inch at 400 yards.

SlamFire1
March 20, 2013, 05:42 PM
for expediency, some people use "Shooter's MOA" SMOA or IPHY "inch per hundred yards" because it's close enough (meaning, their guns aren't accurate enough for them to tell the difference between 1" per 100 yards and the more exact precise measurement.

I have had this discussion with good shooters and new shooters. New shooters think they need an 1/8 MOA sight. Makes sense if you think about it, put on an 1/8 MOA click and geometrically the group should move 1/8 of an MOA.

But the real world is much more confounding. I shot for years with MOA sights out to 1000 yards using a post, now using MOA on the match rifles. I can say for certain that I do see the group move with a adjustment, the court is out whether I always see it move with a , though sometimes it seems to, and I don’t think I would ever live long enough to see the group move an 1/8 of an MOA.

A few F Class shooters might see movement with 1/8 MOA clicks as F class had to reduce the bull to a MOA bull. But based on the scores for the majority of F Class shooters at the last match, I don’t think their scores would have been much different had they been using MOA sights.

Don't sweat the fractions or the round offs based on the match. There are days where you will be lucky if the group moves in the direction you want.

taliv
March 20, 2013, 06:10 PM
i understood him to say he was getting into benchrest, so i figured it might be visible.

i agree it sure is confounding sometimes, but i definitely see my group move with .1 mil adjustments.

N1YDP
March 20, 2013, 06:49 PM
i plan on doing some f class to.i just want to understand my scope.it would be nice to sight in a rifle with two shots. i understand how to get how many clicks per moa.but what i cant figure out is,if i have a 100 yard zero and i want to shoot at 200 yards or down to 25 yards how to do the math.i know 200 yards is 2 moa does that mean i just add 2 moa on my scope?

MtnCreek
March 20, 2013, 07:34 PM
If you’re talking about moving point of impact on target (say you shot, measured w/ a tape and 3” below target).

At 100yds, using IPHY, then you’re 3moa below target. 8 clicks required to make 1 moa on your scope, so you add 3 moa (which is 24 clicks).

Inside of 100 yds (because we’re assuming a standard of 1” @ 100 yds):

At 25 yds, if you hit 3” low, you need 12moa up. 100yds / 25yds = 4. 4 x 3” = 12 moa. Add 12moa to scope (96, 1/8 moa clicks).

At 50 yds, if you hit 3” low, you need 6 moa up. 100yds / 50yds = 2. 2 x 3” = 6 moa. Add 6moa to scope (48, 1/8 moa clicks).

At 75 yds, if you hit 3” low, you need 4 moa up. 100yds / 75yds = 1.33. 1.33 x 3” = 4 moa. Add 4 moa to scope (32, 1/8 moa clicks).

Outside of 100 yds:

At 200 yds, if you hit 3” low, you need 1.5 moa up. 100yds / 200yds = 0.5. 0.5 x 3” = 1.5 moa. Add 1.5 moa to scope (12, 1/8 moa clicks).

At 563 yds, if you hit 3” low, you need 0.5 moa up. 100yds / 563 yds = 0.18. 0.18 x 3” = 0.5 moa. Add 0.5 moa to scope (4, 1/8 moa clicks).

N1YDP
March 20, 2013, 07:40 PM
i was wondering if there was a way to do it without fireing a shot.

MtnCreek
March 20, 2013, 07:42 PM
Data Book with notes showing what your hold is for that bullet in those conditions. You only get that from shooting.

cacoltguy
March 20, 2013, 09:33 PM
As far as sighting in your rifle at a certain distance (lets say 100 yards) and knowing what dope to use for 400 yards (or any other distance), there is no math calculation that will get you 100% dead center on target. You will only know your dope for different distances by shooting it. Different bullets and loads have different trajectories depending on the velocities of your load and bullet type, so you wont be able to sight in at 100 yards and do a quick calculation to know what adjustments to make for 400 yards. However, utilizing ballistic calculators will get you very close, or at least on paper (if you enter the correct data) When I re-barreled my rifle in a different caliber I had no dope for long ranges. I just went to the range utilizing what that ballistic calculator told me and adjusted from there to fine tune it.

This link below is the one I and many others use. You will need to know your muzzle velocity but if you don't have a chronograph, the ammo manufacturers data will at least give you something to start with. Try to enter the anticipated temperature and altitude of your range as well. Leave the wind data and direction blank since you are only trying to get elevation adjustments for now. You will also need to know the ballistic coefficient for the bullet you are using. This can also be found on the bullet or ammo company's website. Of course, with ballistic calculators, they are only as accurate as the data you put into them so the more you know your setup and range conditions the better. I'd say just print out the results it gives and bring it to the range with you. After the match you will have fine tuned it and will have good data to use for the future.

http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi

taliv
March 20, 2013, 11:03 PM
i understand how to get how many clicks per moa.but what i cant figure out is,if i have a 100 yard zero and i want to shoot at 200 yards or down to 25 yards how to do the math.i know 200 yards is 2 moa does that mean i just add 2 moa on my scope?

i have no idea what you're asking. please ask again. what do you mean 200 yards is 2moa?

do you mean you read somewhere that your come up from a 100 yard zero to hit a target at 200 yards is 2 minutes? then yes, if that were true, you would just dial 2 minutes (16 clicks on a 1/8moa turret) up

N1YDP
March 21, 2013, 07:52 AM
yes,i meant 2 minutes,so,i would just and 2 minutes to my scope.

hunttheevil
March 21, 2013, 10:48 AM
You would have to know the ballistic data for the rifle and ammunition you are using. Let's say with a 100 yard zero your bullet drops 3 inches at 200 yards, based on ballistic data. That is the scope adjustment you would have to make to change the scope's zero for point of impact at 200 yards. So knowing the bullet drops 3 inches, you would adjust up 12 clicks per 100 yards, to adjust the scope for the 3 inch drop. I've attached a generic trajectory graph to show a ballistic curve.

Jon_Snow
March 21, 2013, 02:47 PM
although, actually, most people calculate it a different way....

imagine yourself standing in the center of a circle. imagine the target is on the circle. that makes the distance between you and the target = the radius of the circle.

now if the radius is 400 yards, you can use forumula 2 x radius x pi to get the circumference. in this case, 2513.2 yards

now convert that to inches by multiplying by 36, gives you 90475.2 inches. now, divide by 360* means each degree in the circle subtends 251.32 inches. now divide by 60 to get minutes. each minute is 4.188 inches. (as compared to 4" even using IPHY)

so 1/8th of a minute is .5236 inches at 400 yards.

that means every time you click your scope you should theoretically be moving the bullet impact roughly half an inch at 400 yards.

Wellllllll, if you really want to be precise, this isn't correct, because the target is flat. What taliv described is the arc length, while using the sin() of the angle gives the straight line distance. However, small angle approximation says that sin(small angle)~=(small angle) and one (or even several) MOA definitely counts as a small angle, so the arc length and the sin() are approximately equal as well. The differences here are smaller than the 1MOA=1.00" vs 1.04". But you wanted the math, careful what you wish for.

taliv
March 21, 2013, 05:29 PM
to be fair, i did mention the trig method first in post 6

Jon_Snow
March 21, 2013, 05:44 PM
I wasn't trying to call anyone out on that, just being picky about the math.

cacoltguy
March 22, 2013, 02:34 AM
"i understand how to get how many clicks per moa.but what i cant figure out is,if i have a 100 yard zero and i want to shoot at 200 yards or down to 25 yards how to do the math.i know 200 yards is 2 moa does that mean i just add 2 moa on my scope?"

No. All 2 MOA at 200 yards means is that if you adjust your scope 2MOA at the 200 yard line, it will move the impact of the round 4 inches in whatever direction you move it. If you made a 2 MOA adjustment at the 100 yard line it would move it 2 inches. (1MOA=1 inch at one hundred yards, 2 inches at 200 yards, 3 inches at 300 yards etc.) One MOA is one MOA. It just has a larger effect one your adjustments the farther away from the target you are. If you have established your 100 yard zero, adding 2MOA will move the impact of the round up 2 inches. That doesnt mean you will be hitting center mass at 200 yards though. It depends on how much your bullet is dropping and there is no quick calculation to figure this out if all you know is your 100 yard zero. You have to first know what your 200 yard zero is prior to knowing how many minutes of adjustment to make from 100 yards to 200 yards.



I may be misinterpreting his postings, but I get the impression that NY1PD is confusing the math involved with understanding MOA adjustments at one particular distance with making sight adjustments as you go from one yardline to the next. They are two different things. Knowing what MOA adjustments to use for a distance other than your zero distance can only really be known by shooting it. You can't get a 100 yard zero and do a quick calculation to know what adjustments to make for 200,300,400....etc. yards. Different bullets and powder charges will cause the bullet to take flatter or less flat trajectory to the target. The only way to get your starting dope for different yard lines without actually shooting it is to plug the info into a ballsitic calculator like I posted above. Once you get your sight adjustments for different distances THEN you can apply your knowledge of MOA and your scope dials to go up or down as your shoot at different yardlines.

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