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I have a CZ 457 Chassis 16”, CZ At-One 20”, and two Savage MKII TR 24”. All have been pillar and glass bedded by a gunsmith, trigger jobs, free floating barrels checked, experimented with torque values and adjusted for best accuracy. Randolph front and rear. Experimented with clamp force, bag positions, 3 Wick Style flags are always used along with range journal to take copious notes documenting what works and what doesn’t.
I feel your pain, years ago our local clubs started a sporter match, I have always shot heavy target rifles, so the transition to a much lighter rifle with a much less powerful scope was a challenge. I have an older Savage a 23AA, which when I was a kid, I thought it was the cats meow as far as accuracy goes. We were using 12X scopes at 50 yards with bipods only. Well the Savage wasn't cutting it. I was shooting with guys using 54 and 64 Anschutz, 541 Remingtons, CZ 452s and 453s. I bought a 452 Ultra Lux, way better than my Savage, but still not on par with others. I then purchased a new 452 Trainer. This was another step in the right direction, but still not there yet. Then I found a early production CZ 452. Now I was on to something. Like you I was using the lesser grade of ammo in the CZ, SK, Wolf, Eley Team. Later I moved to Eley match, seeming how I had plenty that I used in my Heavy target rifles. I had just bought a couple of bricks that my 52s or 40Xs did not like all that well. I figured rather than selling it, which is what I usually do with lots that don't work for me. I tried it in the older CZ. Absolute game changer, used that lot of ammo for 2 months until I ran out. 1st or 2nd every week. The sporter thing started kinda fell out of favor with several in the group, so we went to shooting Pistols, time to start over. But that's a story for another time.
If I were you, work with the CZ At-one, although I would want a 24" barrel, but that is what you have. Try different holds on your rifle, these light rifles usually don't do well trying to shoot free recoil, mine I would the top of the stock while pinching the trigger. If your shooting using the magazine, try loading one at a time without it. Then try different ammos. Mine liked Eley match, there is almost always plenty for sale over on RFC at reasonable prices. Last suggestion, find a older CZ 452. The way to tell is, either no letter prefix or a A prefix. I don't know what the difference was after B and C models came out, but there is an accuracy difference. JMO
Good luck to to you and re-read post 6. Advice from Tony Harper is valuable.
Best target I ever shot with the older CZ outside 50 yards 12X scope.