Flattened primers in revolvers can be a sign of a little extra headspace. The primer backs out against the recoil shield under the pressure of firing, due to the headspace issue, then the case sets back against the shield leaving flattened looking primers. It only takes a couple thousandths extra on headspace to do this BTW.

A good chrono is the best way short of a pressure gun, to check that your loads are performing in approximation with published data. I have had flattened primers and sticky extraction with loads that gave very near indentical velocities to the data I was using. That is with the same length barrel too. It really does come down to an individual gun's tolerances, smoothness of chambers, throats, forcing cone etc. You may get pressure signs, while not actually going over recommended loads, or velocities. Then again, you may get no pressure indicators, and be well over SAAMI specs. Caution is a reloaders best friend.

One other thing to consider- when your cases are seated in your chambers, are they flush with the rear face of the cylinder, or are they possibly a couple thousandths below flush? That would cause the same appearence of excess headspace. It is possible. Just something else to check for in guns with recessed chambers.