None of the component companies will go into much detail as to their manufacturing of primers, since they all consider it proprietary. The closest thing you'll find to an explanation is this from CCI:
CCI® BENCHREST RIFLE PRIMERS
In benchrest competition, there’s no such thing as a group that’s “too small.” Everything has to be tuned to the highest degree to produce match-winning results. That’s why we make CCI Benchrest primers. Only our most experienced skilled personnel put the priming mix in the cups, so you get the same flame, shot after shot. We also use specially selected cups and anvils for added consistency. An independent researcher identified the use of CCI Benchrest primers as one of two factors that were the most significant contributors to tiny groups. We can’t add much to that!
Remington also refers to their 7 1/2 primer as Benchrest, but offers no description of the process or component parts.
Federal refers to their Premium primers as Gold Medal Match, but does say that standard data should be used with them. Winchester doesn't make any distinction between their primers.
Minus a ballistics lab to do thorough testing, I guess it's up to each person to make up their own mind about what the differences are.
Hope this helps.
Fred