ok it is hard to explane so bare with me I want to make a base for my gun and would like it to be a 15-20 MOA base It has been YEARS since I used Trig and I know it can be figerd out with that but cnat remeber The base I am making will be 6.5" long and would like to know how much differance I need from a ZERO point to the 6.5" mark to make a 15 MOA base and a 20 MOA base........So if i took my diel indicater and zeroed it out and moved 6.5" how much will it travel to get me 15 MOA and then also for 20 MOA

Hope some one on here can understand what i am tring to explane

Well if I did it right at 6.5" a MOA is .00189078" (1.0471996/3600*6.5)

So if i take the .00189 X that by the MOA I want it should give me what I need...so for 10MOA = .0189 and 15MOA = .02835 and 20MOA = .0378

Thanks I will give it a shot and see how it works....

Why make it so hard on yourself? Have you looked for a base on the web to fit your action? Ken Farrell makes many of them...

http://www.kenfarrell.com/index.html

I will book mark his web sight but what I am making the base for he dose not have one made for what I want. I have a .308 Winchester barrle by MGM for my Thopson Center Ecore it is 30" with a 1-10" twist so wanting to make a base for that....

My buddy Rick emailed me the values needed to determine this exact thing.

For a 6.5 inch base, you will need to add .029 to the rear of the base for 15 MOA. For 20 MOA you will need to add .038.

quote:

For a 6.5 inch base, you will need to add .029 to the rear of the base for 15 MOA. For 20 MOA you will need to add .038.

Hey my late night math worked.

Do you remember trig class in high school? Your teacher said, "MagMan, pay attention! Someday you're going to need to know this stuff." Well, that day is today.

Ray

well Cheechako I did not have trig till I was in Collage for Machine tool and never used trig till 7 years latter (Now) that i want to do some gunsmithing

And thanks every one for helping me out I will be getting the base setup tommarow and try and make it out to the rangeg to see how it worked..Just need to make up some loads

I once shot a 1000 yard BR match with a rifle which did not have the necessary cant built into its bases. I used the formula for iron sight correction to figure out how much to add in shims the rear base. This formula is:

(Sight radius)*(error)/(distance)=(sight correction)

All input in inches.

In the case of finding cant for a scope base the "sight radius" becomes "distance between front & rear scope base screw". The "error" becomes the "MOA cant" you desire. I used 100yards(3600 inches) as the target distance as 1MOA basically equals 1 inch at that distance.

Example; you have 5 inches between front and rear base screw. You want a 20MOA base. The math looks something like this:
(5)*(20)/(3600)=(0.0278)

This means you base will need to be 0.0278 taller are the rear screw hole then at the front screw hole.

Or more simply you need a 0.006" per inch taper for a 20MOA base.