To deal with parallax, wouldn't it make sense to make an aperture sight (a ring mounted to a rod in a parallel plane above the jig) so that your angle of incidence and focal distance are always the same? For you old guys, you could even put a magnifying diopter in the aperture. Seems easy enough. Also, would a groove and a quality o-ring reduce bore play to a tolerable level (pun definitely intended)? I've never used an optical punch, but it seems like the shortcomings can be overcome or reduced with a little bit of mechanic-ing.