Need some Math help on Optics

[Lakedaemonian]

So I like the Trijicon RMR. I'd like to get the 7MOA dual illum reticle but its never in stock @ Brownells. The 13MOA is however, always in stock. I want to use the optic in 30yds & in shooting. My problem is that I suck at math. Can anyone tell me how big a 13MOA dot will appear to be @ say 25yds? Better yet, explain why/how you get this number. (Give a man to fish, he'll eat for a day, teach a man to fish, he'll eat for a lifetime.)

 

[SeekHer]

13MOA will cover:
13"/33.02cm at 100 yds.
6.5"/16.5cm at 50 yds
3.25"/8.255cm at 25 yds.

A 4x scope will make the object at 100 yds appear as if it was 25 yds away as seen by the naked eye.
A 6x scope would make it appear to be 16.67 yds away.
A 10x scope would make it look as if it was 10 yds away.

 

[natman]

So I like the Trijicon RMR. I'd like to get the 7MOA dual illum reticle but its never in stock @ Brownells. The 13MOA is however, always in stock. I want to use the optic in 30yds & in shooting. My problem is that I suck at math. Can anyone tell me how big a 13MOA dot will appear to be @ say 25yds? Better yet, explain why/how you get this number. (Give a man to fish, he'll eat for a day, teach a man to fish, he'll eat for a lifetime.)

SeekHer has it right.

To calculate the area a given MOA will cover, use 1MOA = ~one inch @100 yards. So 13MOA x 1 inch / MOA @100 yards = 13 inches @100 yards.

To find the MOA to inches conversion at different distances, multiply by how many times 100 yards the desired distance is, i.e.:

200 yards = 2x100 yards = 2x13inches = 26 inches.
50 yards = .5x100 yards = .5x13 inches = 6.5 inches.

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I got a phone call at the shop from a customer asking about rifle scopes.

HIM: What does it mean if a rifle scope is a 4x-32?

ME: That means it's a four power scope with a 32 mm front lens.

HIM: What does 4 power mean?

ME: That means if your target is 100 yards away, it appears to be only 25 yards away.

HIM: Does the bullet still have to go the whole 100 yards?

Long pause.

ME: Yes, sir, the bullet still has to go the entire 100 yards. The scope merely makes the target look like it's only 25 yards away. It does not actually warp the space-time continuum.

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Build a man a fire and he'll be warm for a day.
Set a man on fire and he'll be warm for the rest of his life.

 

[Sky]

Red dots above 3 MOA cover to much of a target for my preferences. I use them at (red dots) different ranges and if you are covering 3 or 4 inches of target at 30 yards with the dot you may not like it for accuracy...... A target hidden by your dot is not a target easily struck. Works on dog size critters but you can forget rats an other small critters IMO.

 

[henschman]

To figure out how many inches 1 MOA equals at a given distance, take the distance in yards and move the decimal two places to the left.

So for a distance of 25 yards, 1 MOA is equal to 0.25 inches (1/4 inch). Multiply that by 13 and you get 3.25. That is how many inches 13 MOA covers at 25 yards.

 

[SeekHer]

Actually 1 MOA isn't 1" at 100 yds it's 1.04719
The formula is:
(((((r*36)*2)*Pi)/360)/60)=M
r = range in yards
pi = 3.14159265
m = MOA

 

[wally]

I've the 13 MOA RMR on my FNP 45. Its borderline too big for pistol distances, I think you'd be quite unhappy with it on a rifle unless you planned on only using it at 25-50 yards.

But it is very easy to pick up quickly.

 

[Lakedaemonian]

Thank you all. The knowledge & breakdown is much appreciated.

 

[natman]

Actually 1 MOA isn't 1" at 100 yds it's 1.04719
The formula is:
(((((r*36)*2)*Pi)/360)/60)=M
r = range in yards
pi = 3.14159265
m = MOA

You are, of course, quite correct. That's why I wrote it this way:

1MOA = ~one inch @100 yards

The ~ indicates "approximately" or "close enough for all practical purposes, except for the most obsessive nit pickers".

I'm sure the OP is relieved to know that his 13 MOA sight actually covers 3.4033675 inches at 25 yards and not the 3.25 inches we had misled him to believe.

 

[Bwana John]

Real men use radians

 

[trex1310]

ME: That means if your target is 100 yards away, it appears to be only 25 yards away.

HIM: Does the bullet still have to go the whole 100 yards?

LOL. Lord Almighty, I'm not sure if that person should be handling a rifle.