So I received the 6x48 tap for scope mounts. As I explained in another thread, it was done on a bridgeport milling machine with a Digital read out. Makes life easier 
Made a pin to match the diameter of the rear hole in the receiver and indicated from there. Here is a few pics while I was doing it.
Happens it's a .312" hole so just polishing a 5/16 rod to make it slide snug was all it took.
Pin in the receiver
Locating with a collet and fitted pin
Located, touched and compared to the scope mount to make sure everything lined up. Drilled to depth and now taping
Need to clean up holes before testing
Looks like it's gonna work
Here it is with a micro dot sight.
Made a pin to match the diameter of the rear hole in the receiver and indicated from there. Here is a few pics while I was doing it.
Happens it's a .312" hole so just polishing a 5/16 rod to make it slide snug was all it took.
Pin in the receiver
Locating with a collet and fitted pin
Located, touched and compared to the scope mount to make sure everything lined up. Drilled to depth and now taping
Need to clean up holes before testing
Looks like it's gonna work
Here it is with a micro dot sight.
