I would need a lot more information. Are you using a mechanical rest, physical rest (like a sandbag or "notch"), or shooting freehand?
Even mechanical rests seem to be "load sensitive," from what I can tell. I've never had access to a Ransom Rest, the proper parts/inserts, and a CZ at the same time.
An acquaintance who belongs to my range has a Ransom Rest, but I've only used it with K-frame S&Ws at 25 meters. We found that many of our "pet loads" actually group better from a physical rest or shooting freehand, even at longer ranges. My theory is that a nearly perfect load developed by a particular shooter with his/her own equipment and components will actually shoot better in his/her own hands. In other words, that shooter's individual technique and idiosyncrasies, along with using the same exact equipment an components, are what made that load nearly perfect in the first place.
1.6" group, depending on how you measure it, would be considered acceptable with any handgun at 25 meters. If you are measuring dispersion from POA, that is pretty good for a service pistol, even from a mechanical rest. If you are measuring the actual group from point-to-point from a mechanical rest, then not so much.
Shooting freehand at significant distances seems to be more dependent on the sight picture/covering of the sights, individual techniques (such as trigger control), and confidence, rather than the actual characteristics of the pistol. Most pistols are not designed to shoot at 25m, due to the limitations of the sights.
