foxy,
I had the same problem with my 452. Always the first round from a mag, the rest went into one hole. In my case it was about 1.5" low and left. It wasn't really a "cold" bore problem. You could shoot 15 rounds let the gun sit for 10 minutes put another mag in and %$*@ the first round was and inch and a half out. I tried different ammo from cheap to hi $. I tried carefully torquing the action screws. I tried everything I could think of short of bedding the action. Spent lots of time with the gurus on Rimfire Central. All with no success. Finally, since it was always the first round out of the mag, on a hunch I tried single loading with CZ's adapter.
Problem solved. No more flyers. The gun will rounds 1 thru 10(or 15 or ...) into .25" or less at 25yds. Hot, cold, in between - it doesn't matter. It will do it with Federal 510 and with Wolf Target. The Wolf does group a little better at 25 and quite a bit better at 50 and 100.
I've tried loading a mag and cycling the cartridges through it. I don't see any noticable difference between the first out and the rest. For the life of me, I don't know why it works for me. What I can assure you is, it does.
good luck