OP, what kind of ammo are you using for zeroing? Surplus ammo is, shall we say, not known for consistent accuracy
I don't know how much you know about zeroing sights, but the CZ type rifle (along with the SKS and AK pattern) adjusts the front sight to confirm elevation on the back sight and also adjusts for windage. When sighting in with the front sight, you must remember that the sight must be moved in the
opposite direction you want the bullet impact to move (i.e. - move the sight left to move the impact right, and move the sight down to raise the impact-definitely NOT intuitive lol).
Use good ammo and good luck!