Help with some MOA math

[Fairchaser]

What’s the equation for how much the scope reticle moves for 1 MOA? Another way to ask is how much does the angle of the barrel move for 1 degree in inches or thousands?
I’m trying to understand how little or how much the barrel moves to change the POI down range. Is it 1/60?

 

[Mike Casselton]

Barrel length matters if you're measuring from the muzzle.

I wouldn't try to do that math, I'd look at it in degrees of elevation instead.

Honestly though, I'm not sure why you're even trying to figure it out.

 

[AccelR8]

This may help

Gun Sight Correction Calculator

 

[L.Sherm]

.

 

[Fairchaser]

How much movement at the gun will move the poi down range 1 MOA? I assume it’s 1 degree but how much is one degree? 1/360?

 

[xr650rRider]

1 minute of angle is 1/60 of 1 degree. If your shooting at 100 yards, that's 3600 inches.
Tan(1/60)*3600=1.0472"
So when you move the sight 1/60 of 1 degree, you move 1.0472" at 100 yards.

 

[AccelR8]

How much movement at the gun will move the poi down range 1 MOA? I assume it’s 1 degree but how much is one degree? 1/360?

360 degrees in a circle. 60 minutes (60 Minutes Of Angle) in a degree. 60 seconds in a minute.
So to move 1 MOA you're moving 1/60 of a degree

 

[AccelR8]

Using that sight calculator I linked earlier; if we assume inside the scope, the distance of the pivot point, that is the spherical joint for the inner tube holding the reticle is 3.5 inches from the adjustment mechanism, the turrets, to move the reticle 1 MOA the reticle moves .001” which is not very much!

Of course I could be interpreting this incorrectly...someone tell me if I’m wrong.

 

[dhagerty40]

since I retired, I hate doing all that fancy math!

but this might give you some hints:

What is Minute of Angle?

Minute of Angle (MOA) is an angular measurement, used often in long range shooting, that is 1/60th of one degree of a circle.

www.nssf.org

 

[Albany Mountain]

An iron sighted rifle with approx 26 inch barrel will have the rear sight move about .008" for 1 moa.

 

[xr650rRider]

An iron sighted rifle with approx 26 inch barrel will have the rear sight move about .008" for 1 moa.

That would mean the sights are 27.5" apart. .008"/Tan(1/60)=27.5"

 

[Jeff Porter]

on a 20" barrel AR A2 iron sight it is about 0.006" - the actual distance moved will vary on the length of the aiming system.

since you are asking about a scope reticle... that is a very small distance per MOA inside the tube. might be easier to figure out thread pitch on the knobs and calculate from that.

 

[SG4247]

Agreed, the actual sight radius on a peep and post open gun, is much larger that a scope rifle where the distance from your eye to the scope reticle is like only 6-8” or so.

So, the scope reticle vertical movement is very small in comparison to a rear peep iron front sight aiming system that has 26” in length.

I have all the trig calculations for scope reticle movement and bbl angle change for 1 MOA at 100 yards, on a note pad if you are interested.

It looks like a couple thousandths of an inch reticle movement in my calculations.

 

[Fairchaser]

Thanks for sharing these answers to my question. I think it’s helpful to understand how important gun handling is down range when that little movement can move you out of the 10 ring.

 

[AccelR8]

since you are asking about a scope reticle... that is a very small distance per MOA inside the tube. might be easier to figure out thread pitch on the knobs and calculate from that.

Well, a simple micrometer has a thread pitch of 40 treads per inch. One revolution is therefore .025 inch. Coincidentally, looking at the nearest MOA scope, it has 25 minutes per turret revolution. If what I posted in #8 above is correct, then we can assume the turret thread is 40 tpi. and one MOA inside the scope is .001"

I do not volunteer to take my scope apart and measure!

 

[dcali]

It sounds like a very tiny amount - .005 or so", but when you consider that the aperture in a service rifle (for example) sight might be .050, it seems like quite a lot - something you can easily see.

 

[OLeveraction]

This stuff always makes me laugh.
One actually sees the change of barrel angle using a good prep sight.

 

[creedfan]

Not sure if I understand the question but assuming its a 28 inch barrel .008145 would equal 1 MOA

 

[Darryll]

This is a very basic over-simplification. I think of MOA as a funnel. If you can shoot a 1-inch group at 100 yards, it roughly opens up an inch for every 100 yards of distance increase. 1 inch group at 100 yards will be a 2-inch group at 200 yards, 3-inch group at 300 yards, and a 10-inch group at 1000 yards. This doesn't take wind, drift, bullet drop or anything else into consideration.
Like I said this is a very basic oversimplification that depends on way too many variables, but this helped me understand the basic concept.
I hope that this helps. I'm sure if I'm wrong that someone will be polite enough to correct me.
Darryll

 

[davidjoe]

This stuff always makes me laugh.
One actually sees the change of barrel angle using a good prep sight.

And in my opinion a good match director should spot gross barrel angle errors and correct that issue on sight, imo. There is viewpoint against all coaching, but safety first.

32 moa up on a .308 at 1,000 over 100, does not mean the bullet peaked some 320 inches high, though.

It’s not the OP’s specific question, but bullets rise to a peak of about 35% of the height suggested by a long range come up.