Gunsmithing making a 20 MOA scope base rail question

[chpprguy]

I’m trying to make a 20 MOA picatinny rail for a friend of mine…
(he loves Ruger M77 MKII’s, and I cannot find a base)

So, I want to see if my attempt at math appears correct…

1 MOA is 1.047” @ 100 yds…

3600 inches in 100 yards….

1.047/3600 = .000290833333

.000290833333 x 20 = 0.00581666667

So… approximately .006” negative off set per inch of rail length

should get me close to 20 MOA????

am I crazy, or should this work?

 

[chpprguy]

Re: making a 20 MOA scope base rail question

I used a cheat, and I think I am close...

 

[AXEMAN]

Re: making a 20 MOA scope base rail question

not sure about the math, but have you tried EGW?

 

[chpprguy]

Re: making a 20 MOA scope base rail question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: AXEMAN</div><div class="ubbcode-body">not sure about the math, but have you tried EGW? </div></div>

I haven't asked them, just looked at their site and one isn't offered...
Ken Farrel makes a mount for SA's but not LA's....

 

[chpprguy]

Re: making a 20 MOA scope base rail question

no mathematicians in the house to tell me if I am close or not?

It sucks to make chips when your math is wrong.....

 

[300sniper]

Re: making a 20 MOA scope base rail question

i think you are right on. i came up with .0058" taper per inch.

 

[chpprguy]

Re: making a 20 MOA scope base rail question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 300sniper</div><div class="ubbcode-body">i think you are right on. i came up with .0058" taper per inch. </div></div>

ok, thanks....

 

[Rhys]

Re: making a 20 MOA scope base rail question

The math is good.

 

[Lindy]

Re: making a 20 MOA scope base rail question

Another way to look at the nice picture is that tan A = a/b.

In this case, b = 1, so tan A = a

Or a = tan A

Now, 20 MOA = 20/60 degrees, so A = 0.33333 degrees

The tangent of 0.3333 = 0.005818

So, your math is correct - and now you know the correct method for calculating it.

 

[chpprguy]

Re: making a 20 MOA scope base rail question

Thanks,

and Lindy's way is easier....

 

[krlemas]

Re: making a 20 MOA scope base rail question

Scope base
Dan Lilja wrote an article about this, maybe it might help.

Ken

 

[nervous]

Re: making a 20 MOA scope base rail question

X / R = D / 3600

Where:

* X = Required change in sight (inches)
* R = Sight Radius (inches)
* D = Difference (in inches) on target (100 yards away)
* 3600 = 100 yards (converted to inches)

Nervous

 

[Lindy]

Re: making a 20 MOA scope base rail question

That's handy if you don't have a trig calculator around.

In this case, when solving for the change per inch of base, it reduces to:

X = D / 3600

But you do have to multiply the desired MOA change by 1.047 to get D.