CALCULATING CANT FOR SCOPE RAIL MACHINING

[SS GO DEVIL]

Ladies and Gentlemen,

After about an hour of trying to figure out the calculation for a scope base I came to the final figures and an easy way to figure the height needed for accomplishing the right height for particular actions.

Calculations below (make sure your scientific calculator is set to degrees and not rad!)
Going to use example of 20 moa

1. 20 moa / 60 = .3333333333
2. .333333333 then hit tan = .005817829810955
3. .005817829810955 x scope base length (6'') = .0349069

So when machining or shimming a scope rail the rear of the rail needs to be .0349 higher than the front.

Enjoy and hope this saves someone some time at some point.

 

[Ggmac]

That .0349 is only going to work for the 6" spacing / base .

 

[carlsbad]

20 moa = 1/3 degree

Tan (.3333) x 6" = .0349"

Better living through trigonometry.

Generally: tan (.33333) x (spacing of your measuring points) = Raise

I do my daughter's advanced geometry in my head while cooking dinner so if I can ever be of help with geometry I'm glad to. I've figured out that some modern calculators like you to hit tan before typing in .333333". Which is backward.

--Jerry

 

[Fast14riot]

20 moa = 1/3 degree

Tan (.3333) x 6" = .0349"

Better living through trigonometry.

Generally: tan (.33333) x (spacing of your measuring points) = Raise

I do my daughter's advanced geometry in my head while cooking dinner so if I can ever be of help with geometry I'm glad to. I've figured out that some modern calculators like you to hit tan before typing in .333333". Which is backward.

--Jerry

You sound like me, helping all 3 of my kids with their math in my head while cooking dinner, lol!

For rails, I prefer 15moa, makes the math easier, too.

 

[carlsbad]

I've wondered about 15 moa being better for shooting less than 1000 yards, or even 10 moa. Keeps you closer to the optical axis of the scope where it is sharpest. 20moa putts you 20 moa away from the optical axis at 100 yards. 600 yds is only 12 moa or so, putting you still 8 MOA from the optical axis. --Jerry

 

[AlaBusa]

Easy way for example a 20 moa rail.....20x1.047÷3600=.00555556 per inch.

Multiply the cant of rail by 1.047 then Divide by 3600 and it gives you the fall by the inch. Then multiply by length of the rail.

 

[SRM]

I get .0055” per in for 20 moa

 

[Bully]

I'm either going to go to sleep or my head will explode...

Math...

I know it explains the known universe but damn, it's rough stuff for me.

 

[carlsbad]

Bully,
That's why I offered to help. I know there are math people and non math people. Always available. --Jerry


PS: It has been said that there are only 10 types of people in the world, binary and decimal.

 

[DickE]

Make it easier still 1' scope rail, shoot 100'

 

[Fast14riot]

I've wondered about 15 moa being better for shooting less than 1000 yards, or even 10 moa. Keeps you closer to the optical axis of the scope where it is sharpest. 20moa putts you 20 moa away from the optical axis at 100 yards. 600 yds is only 12 moa or so, putting you still 8 MOA from the optical axis. --Jerry

I went with 15moa just for that reason. My 260AI needs only 24moa from 100 yard zero to reach 1000, so for mid range and LR I'm staying closer to the optical axis, without having to go with taller rings to "flatten out" my dope.