Here is the gun and the symptom:

Regulation Police, 38 S&W, five shot. ~1920.

Symptom - if the ejector rod is too loose (backed out) the cylinder locks up. Duh, I know that one.

Odd symptom - if the ejector rod it tightened down all the way the cylinder is a pain to open and close! I've never hear of this. There is a sweet spot - not too tight and not too loose - where the gun works! I don't like this and feel that good and tight is right.

It is an old rough gun, perhaps some parts have been switched. Could the center pin bee too long?