They are see through overlays with the rings and clearly define the relationship of the bullets meplat with in or out of each ring. They were all marked ASSRA and I would think that is who originally provided them at some cost.

I did a goggle search.  About all I found was a few targets and generic overlays.  We have some plugs with a magnifying lens that we use occasionally.  I usually just place the target over another target.  It is usually clear as to where the center of the bullet hole is in relation to the ring, but I'm not scoring national records 

One of there days, I'll go down and see if I can watch the bench rest shooters measure groups.  Anything over .010" is out of the game!  Way more precision than anything we ever do with PB cast bullets.