Make your base 20-30 MOA in 20 minutes

[brasse]

Took my cheap Ironsighter full length weaver/picatinny rail for short action and made it 20 MOA down in just a few minutes.
Measured the base at the front and rear, both 0.310 inches thick. Used my spare reciever as a mandrel, using sandpaper to first get front and rear of the bases as close to the same diameter as the reciever. The outside of the base bottom was high by over 0.010 inches. Then worked on front base area until is was 0.290 inches thick, finishing up with 2000 grit paper.

Copied from somewhere else
"Making 20 MOA scope mounts
The idea is that a degree is broken up into 60 minutes. The 20 minutes you wish to move your group is therefore 20/60 degrees, or 1/3 of a degree.

The tangent function is simply the slope of the angle (rise/run). No matter how large the triangle, the slope will be the same. In this case, a triangle 1/3 of a degree will rise 0.005818 units for every unit of run (regardless of what unit you're using).
So you plug into your calculator 20 (minutes of angle) / 60 (minutes in a degree) then hit "tan". It spits out 0.005818. So for every unit of run, a 20MoA angle will rise 0.005818 units.

In this case the run (base side of your triangle) is measured from your front ring to your rear ring. So you multiply that run by 0.005818 to find the rise, which is how much you shim.

In my example, if your scope mounts are 5" apart you'd shim it 30 thousandths.

The rule of thumb seems to be .001" equals 1 MOA [the Sighttron instruction sheet may have a chart showing this ]. A .020" shim under the back of the base would be a 20 MOA correction. A .015" shim would be 15 MOA. Not a lot of difference, and you probably wouldn't be able to tell the difference in actual use.
"

[thomae]

If you used sandpaper over a receiver to sand the bottom of the receiver, how thick was the sandpaper and did you compensate for the difference in the radius (between radius of receiver and radius of receiver plus sandpaper) of the curved surface you were sanding?
Also, if you only lowered the front, and didn't angle the back a corresponding amount, wouldn't the mount not have full contact with the receiver?

I'm not disagreeing with you, but simply wondering. I am guessing that if you bedded the mount you could take care of these issues.

[brasse]

"used sandpaper over a receiver to sand the bottom of the receiver Actually the mount base

I was using 800 on the front same time I was using 2000 at the back. I checked the contact area, it was a very slight angle down.

Checked the contact area with dye, nearly 90% coverage where it counts.

[thomae]

Good for you, you listened to what I meant, not what I said.
Thanks for catching the typo...I did, in fact, mean sanding the bottom of the mount base.

I deserve this:


Anyway, I like what you have done. Very interesting. Thanks for addressing my questions.

The proof of the pudding is in the target. I look forward to pictures of your success.

[brasse]

I always appreciate your comments on this forum, your knowledge helps everyone.

[derrelw]

Good for you, you listened to what I meant, not what I said.
Thanks for catching the typo...I did, in fact, mean sanding the bottom of the mount base.

I deserve this:


Anyway, I like what you have done. Very interesting. Thanks for addressing my questions.

The proof of the pudding is in the target. I look forward to pictures of your success.

That's an Orangutan not a chimpanzee

[iusmc2002]

I was just going to post about something like this. Was going to ask what the depth difference was for a 20MOA base, compared to a regular base.
I really like JB Weld for some reason, so I built up the area around my rear scope mount with some thick tape, then put a 35 thou. feeler gauge under the front of the one-piece Weaver mount. Put some JB on the rear half of the scope mount, let it set up for 24 hours, then pulled it off and used JB to fill the spot where the feeler gauge had been. Waited 24 hours and then bedded the front of the scope mount to make up for the angle caused by the rear being higher than normal. I had to fix a couple mistakes because I didn't put any sort of filler in the scope mount's screw holes, and when I ran a drill bit through them, it took a chip or two out of the bottom part of the JB.

It took me a couple days, but it was something to do while waiting for 2 feet of snow to melt so I could go shooting. Can't wait to see how different my POI is with this ghetto set-up....if the snow ever melts