Calculating scope base angle

[roysha]

I am making a special base for a peculiar application and would like to know how to calculate the angle of the base to achieve the various MOAs. I am assuming there is a formula that will allow me to set my milling device at "X" degrees and mill off the bottom of the base to achieve what I need.

I have Googled this and since math is not my strong suit, I'm more confused than ever. I am hoping someone has a simple, understandable method to figure this out.

Before anyone tells me there are hundreds of bases and such, out there, yeah, I know, and would gladly not go through the rigamarole of custom making one, but there is nothing that will work in this instance. As I said, it is an unusual, oddball, situation.

[country gent]

About the most you can go is 20 mins elevation with this some calibers wont zero at 200 yds. but it gets a good head start on the extended ranges. The easiest way to machine your base is on a sine plate or Bar. I started mine with a 1/8" hole on X Y center this was used to set up zeros when changing set ups ( flipping from top to bottom and such) The hole can be indicated in and its there.

You need to know the center of the rolls on your sine plate bar then its simple trig and the machinists handbook to know how much to put under the roll.

Also mark one end of the base to keep it in the same plane flipping it you end up with a flat base.

I made the scope bases sight mounts for my AR flat tops with 20 mins elevation built in for the scope. They work great and help keep adjustments centered.

If your making 2 piece blocks a bar with the spacing to bolt them to and then onto the sine bar makes it easier to do. This also allows them to be set in the same plane so you have a true angle on the blocks not a step in height. SOlidere set up and less ring lapping needed.

[Pirate69]

This may help.

https://www.calculator.net/right-tri...v=&x=Calculate

Example: If you want to mill a base that has a 20 MOA slope, the rise in elevation (opposite side of a triangle) would be 20.94" at 100 yards (20*1.047). The run (adjacent side) would be 3600". A slope of 0.0058" rise per inch run. Plug 20.94" into "a" and 3600 into "b" and an angle of 0.333 degrees in found. I think this is the angle to mill the base from one end to the other. My best guess.

Took another look at this. Assuming the base is 4" long, the muzzle end of the base would be 0.0235" higher than the rear of the base; if cut at a 0.333 degree angle. Hope my calculations are correct. Maybe others have some data on base angles and different in end heights that they can share?

[Cap'n Morgan]

MOA is a constant value, found by dividing 1 degree with 60, which gives 0,0166.

All you have to do is multiply this number with the number of MOAs you want, and you now has the angle.

[Pirate69]

MOA is a constant value, found by dividing 1 degree with 60, which gives 0,0166.

All you have to do is multiply this number with the number of MOAs you want, and you now has the angle.

So, if you take 20 MOAs times 0.0166; you get a calculated value of 0.332 degrees. Looks like good agreement. I took the hard road to get the results.

[Cap'n Morgan]

So, if you take 20 MOAs times 0.0166; you get a calculated value of 0.332 degrees. Looks like good agreement. I took the hard road to get the results.

No need to make it harder than it is.

On the other hand, it took a a bit of trigonometry to work out the elevation-scale for my 1885 High Wall replica, based on the boolit drop at various ranges...
So far, I haven't got around to test if it actually works as intended.

[Pirate69]

That is a great looking setup. I hope the data we provided to roysha will answer his questions.

[405grain]

"Assuming the base is 4" long, the muzzle end of the base would be 0.0235" higher than the rear of the base"

This might seem counterintuitive but, if you raise the front of the base the scope will now be pointing higher, and to get it onto the target you will have to aim the rifle lower. Raising the front of the scope mount will give you a decrease in MOA, not an increase. To increase the MOA of a scope mount you need to make the back of the mount higher, not the front. With the back higher the scope will be pointing more downward, and to correct this the rifle will need to be aimed higher.

[Cap'n Morgan]

This might seem counterintuitive but, if you raise the front of the base the scope will now be pointing higher

A quick trick for moving the open sights on a rifle or pistol in the correct direction - whether it's the front or rear sight - is to imagine moving the chosen sight a couple of inches and then mentally align the sights. It is then easy to "visualize" where the barrel would be pointing.

[Pirate69]

"Assuming the base is 4" long, the muzzle end of the base would be 0.0235" higher than the rear of the base"

This might seem counterintuitive but, if you raise the front of the base the scope will now be pointing higher, and to get it onto the target you will have to aim the rifle lower. Raising the front of the scope mount will give you a decrease in MOA, not an increase. To increase the MOA of a scope mount you need to make the back of the mount higher, not the front. With the back higher the scope will be pointing more downward, and to correct this the rifle will need to be aimed higher.

That is correct. I got that backwards.