Any idea why they were designated seconds?
aesthetics
Not sure that is always the case.
I read an article by a bullet manufacturer a long time ago, and in it they described seconds as either aesthetics
OR something was wrong with the bullet shape specs due to problems with the initial die set-up when switching-out the line to a different bullet production. Consequently, the initial batch (or two) is screwed-up spec wise.
For example the ogive may be inconsistent which would result in inconsistent distance from the lands of a loaded round. However, if one is measuring OAL length based on the ogive (not the tip), this would be easily determined.
Or the bullet based is screwed up, etc, etc, etc.
Bottom line, a visual inspection may discover an aesthetic issue, but measurements are probably required to determine a spec issue.
So if a gun & load combo goes from shooting in the 2's to shooting in the 5's, that may be a tip-off.
But, if they are shooting 1/2" groups, many meat eaters won't care, eh?