making a 20moa rail (from a std rail)

So I grabbed a cheap (NCStar – I said cheap, didn’t I?) dovetail to picatinny adapter for my Condor. It was a bit too wide, so I had to narrow the base a bit, and I figured while I was at the mill, I’d make it a ~20MOA base.

20 MOA is 1/3rd of a degree, so the sine of 1/3rd degree. If I propose to hold the base in the milling machine vise and angle it by propping up one end, approximately 5″ from the pivot point (the end of the parallel at the low end), the amount I need to raise the other end is (5sin.333) or ~0.029″. So, by placing a shim of the proper size about 5″ from the edge of the parallel (where the other end will sit), I get my spacing. Here’s the setup:

Then just wack off the bottom clean, and it’s done:

A quick check at two points (eyeballed) 5″ apart verifies the operation:

Now, if you do nothing else, the mounts for the dovetail will likely force the base to move ‘higher’ and sit with a gap between your carefully machined base and the base of the rifle, so a ~0.030″ shim is necessary between the base and the rifle when installing. (Just figured this out today…)

Harder to describe than to do, the entire operation takes all of five minutes if your mill is set up with a vise.

GsT