Rifle Scopes Base MOA verification formula?

[03psd]

I’ve heard the factory base on the RPR aren’t always the 20 MOA as advertised, sometimes being almost half as much. Since I had mine off to torque and thread lock the mounting bolts I figured I would measure it. I have .0425” difference between the 2 ends. If the base is 7.25” long, what is the formula to determine the amount of MOA machines into the base?

 

[AIAW]

1 MOA over 1 inch will fall: .000291"

.000291 X 7.25 X 20 = .0421"


This also works:

MOA/60 = Degrees

TAN(Degrees) = T


T X Z = difference between front and rear measurements - A and B  (.0425" in your case)


Note: [Z = Distance between A and B measurement points - 7.25" in your case]

 

[03psd]

Yeah, that's about right then, maybe a little over (22 MOA) according to the calculation but those measurements have to be taken super-critically also. They are almost never dead nuts on either way. Usually designers just use 3600" instead of 3769.2" (SMOA versus "True" MOA) which will cause variance also.

Here is what I have used in the past.

L/3769.2 = D

D X M = Thickness difference between rear and front of rail


L = Length of Rail (inches)

D = Difference per MOA (inches)

M = Suspected MOA

If someone has a better method I wouldn't mind seeing it either though.

Thank you sir but this doesnt exactly make me feel real warm and fuzzy. I guess I dont know or appreciate how close "close enough" should be. Playing around with the formula it seems my base should be anywhere from .4 - .75" longer (or more appropriately less sloped) depending on which number you use for MOA (3600 vs 3769). This seems to be a significant amount to my uneducated way of thinking.

In the end it really doesnt matter in my case because once you zero its done and accounted for, whatever it is. I guess the only issue would be if you need the added adjustability on a real long range rifle and instead of getting 20, 30 or 40 additional MOA (whatever the base was supposed to add) put back into your scope thru the use of the base, you got something considerably less.

 

[AIAW]

Yeah, evidently the original method I posted is a bad way of doing it. I always just used it to "rough" guess what the slope was. It seems it's just much easier to use a constant. In fact, I'll just edit my original post to get that rough formula out of the public's way.

1 MOA over 1 inch will fall: .000291"

.000291 X 7.25 X 20 = .0421"


This also works:

MOA/60 = Degrees

TAN(Degrees) = T


T X Z = difference between front and rear measurements - A and B  (.0425" in your case)


Note: [Z = Distance between A and B measurement points - 7.25" in your case]

Lines up almost perfectly with your measurement using both formulas.

 

[strikeeagle1]

Looks like yours is spot on for a 20 MOA.

 

[AIAW]

That's a good bit prettier than my scribbling!

 

[Douglas-001]

I was waiting for someone to say he should have bought a 20 MIL rail or something like that.......