There was a thread on this subject a while ago.
I used the last of my "old blue box" Winchester .22 subs a week or so ago. My CZ 452 was incredibly accurate with them. So picked up some more, that are now in the re-vamped black box. The accuracy is dire with these, so I concur with op about something changing
My rifle is zero'd at 50 yards, and the blue box subs dropped 5.75" at 100yds. Yesterday, I checked zero, at 50, then pushed out to see what the drop was at 100. It was 2" lower than previously, at 7.5". I tried Eleys a while ago, and they were very good, but quite tight to chamber which I am uncomfortable with. So I guess its go on that, "find a make that suits your rifle" panto!!
The annoying thing is the limited shops round here, don't seem to stock anything else Why do manufacturers change things about when its all going well