Originally Posted by dennisinaz
It has a flat rear portion with a lateral groove machined through it.


That base would be for the Springfield 1903A3.

From:
http://www.milsurps.com/showthread.php?t=1584

[Linked Image]

---------------------------------------------
Since there were no factory drilled holes, the different manufacturers of scope bases made their own decision on hole spacing. You will probably have to find the right make of base to fit your holes.

Or mount two piece bases. The rear base can probably use the hole already there for one screw. The front base may or may not match the hole spacing. Different brands may have different spacing, for the same reason as the one piece bases.

I think the best method if nothing fits close enough is to find a base that fits the contours, then have the base holes welded closed and re-drilled to match the receiver. This can be done with "blank" bases without holes, if you can machine the bottom contour.

Bruce