Aardvaark, you may have to bed the action, in your rifle, CZ 527 don't come very well bedded,, at least the 4 I have didn't, I've had to do two, of mine, one was bought new, wonky,wobbley in the action to stock, for cheap.
Try using the set trigger, this may also improve groups, off the bench,
Both Cz .17 hornets I have are consistent 3/4 five shot group's, the varmint is closer to 1/2", very small powder differences, make a big difference in speed, 1/10g make change things by 50 fps.
I recommend weigh each load, at least during development,
I also agree with elk above, that magnum primers are not at improvement, if your getting overpressure ruined cases, drop back your H4198 loads, throw away little gun, I had blowen primers at minimum littlegun charges,
Blackout, N120 h4198, 4227 are good powders to start with,
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