This is a quick jig i made to hold an AR15 level for engraving. It has been designed with mounting points 75mm on center to match an X-Carve CNC wasteboard. Two of the M5 thumbscrews are used to secure the jig, the third M5 thumbscrew goes through the magazine catch hole to seat and secure the receiver.
Before engraving it is essential to utilize a dial indicator on your spindle to verify the receiver is true. I shimmed the jig with sheets of paper to get it perfect.
Lastly, it is important to mention this is not a production jig, I made everything loose primarily because the point of the jig is to get the receiver flat, not for a precise X/Y location. The contact surfaces are designed so both A1 and A2 receivers will seat properly.