Help with sight base MOA formula

[300meter]

I am going to machine a custom set of sight bases for a Remington 700. Does anyone know the formula for calculating the taper, given the amount of moa you want to build into the bases? Looking to have 20 or 25 moa taper. Don't really want the answer, I would like the formula so I can use it again in the future. Thanks for the help!

 

[p17enfeild]

it applied trig
so you have your angle .33 of deg(=20moa)
20moa =.333deg
opsite =150mm(should have said earler that this is the lengh from the outer end of the base or top of base)

adjacent =?? ? ?=x

tan = opsite /adjacent
tan.33 =150mm/ x
tan.33x150 = x
.005759x150=x (note .005759 is what calulater give you for tan.33)
.86mm=x

hope this helps is metric sorry but formular is same in english .
this tell you how much lower the front needs to be

''edit ill just add .86mm converts to .033inch '' i addded the edit as idnt know how widly used metic is in the US

 

[300meter]

I think I have the answer. Let's say you want to build 20 MOA into a sight rail for a Rem 700. You convert 20 MOA to degrees which is approximately 1/3 degree. The sine of 1/3 degree is .0058177. Multiple that by the length of the rail which is 5.410. This gives you .0314737, rounded to .032 which is how much higher the rear of the rail needs to be compared to the front.
Anybody care to confirm or comment?

 

[p17enfeild]

yes you got it but tan seem to work out easier for me but both work
if you dived the moa required by 60 tis give the degrees in decimal so you got
20moa /60moa =.333.....degrees

 

[woody_rod]

The other way is straight out measurement:

0.010" per MOA @ 36 inches length. 12 inches of length (in your mill say) gives 1/3 of this or 0.0033". This works out pretty well as you can do it via a simple vernier measurement.

 

[300meter]

Thanks for everyone's input. I had help with my math and thought I would share it, just in case it would help someone else.

 

[DickE]

Well I'll just figure in inches. if your scope base is 4" front to rear, that is 1/3 (.333)foot. So, if you raise the rear by .010, that is .030 in one foot. 100yds is 300ft. so multiply.030X300=9"
.015 x 3 = .045
.045 x300=13.5" You should see the logic. and an easy formula.

 

[hawghunter]

Can this formula be put in the articles section for future reference for anyone else who mite need it thanks

 

[300meter]

That would be a great idea to post this in the articles section. But we need a standard solution/formula for this math problem. There are really 4 different ways of arriving at the answer currently posted. At least one method arrives at a different solution than the rest.

Any mathematicians up to the challenge of an accurate and exact formula?

 

[DickE]

Well here's my formula in inches.
1. Length of scope mount(decimal)/12 = decimal of a foot.
2. Desired rise of point of impact (in inches) at 100yds./300 = rise
3. length of scope mount(decimal) x rise= rear (rise)offset or shim to the rear of scope mount.
How's that.

 

[DickE]

That's not all you need to know. Remember your front radius of a Remington 700 is .676 (approx.) 1.352" diameter, and the rear portion of a Remington receiver is approx. .100 lower, and a radius of approx 2.00", a 4"diameter profile on top.

 

[Clark]

An easy way to think of it is slope, like on a roof, it is "rise over run" = rise/run

The slope of 1 moa is 1" up at a target ~100 yards away.

100 yards = 300 feet = 3600 inches

So the slope of one moa [minute of angle] = 1"/3600" = ~ .00028

So if the scope mount is one piece, 6" long, and you want 20 moa higher point of impact, then the rear of the scope mount must be raised:
H = [20 moa] [.00028 ] [6" between mount contact points] = .034"

If the mount touches at the front, and the shim is added 5" behind that around the screw, then the thickness of the shim becomes:
H = [20 moa] [.00028] [5"] = .028"

The best way to do this is with tiny pieces of tape.
Then verify at the range or on a bore sighter that the change is correct.
Then put epoxy between the mount(s) and the receiver, with the mount screws loose
Verify again that the scope is aligned correctly while the epoxy is soft.
When the epoxy is hard, tighten the scope mounts with Loctite.