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?

I had the same problem on a 38 Terrier I took just a bit off the end that latches to the barrel locking lug take it slow testing often for proper fit.

To test the length of the rod. Tighten it down and with cyl open, push something hard and flat against the rear tip of the ctr pin until it's flush with the ratchets.

Hold it there and look at the front end. The ctr pin should stick out of the rod ~ .003" to .005" to open smoothly. If not take some off the end of the mushroom knob being sure to keep the end square to the rod.

__________________
Jim
S&WCA #819

Usually this problem occurs when the center pin is too short and the bolt doesn't travel far enough to push the center when the cylinder release is pushed forward.

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NEVER GIVE UP YOUR GUN

Don't mess with parts that aren't broken or worn.

Get a new center pin that's the correct length for the model,the one in your revolver is worn too short or someone messed with it.

I don't know if common I frame 32 Regulation Police parts are interchangeable with the 38 Regulation Police.
Smith & Wesson Revolvers 32 Regulation Police (I Frame) Parts

__________________
NEVER GIVE UP YOUR GUN

They aren't. The 38 I frame cyl ctr pins are unique.

From OP's description of symptoms, they are indicative of a very minor issue, not requiring new parts.

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Jim
S&WCA #819

As Jim has said new parts are not needed. I should have clarified which part I shortened. Jim is correct the pin isn't the problem it is the knob it is just a little long once I figured out the problem on mine it took very little work to correct it.

Check the end-shake on each chamber. If there is excess movement from front to back on some of the chambers but not all of them, the front of the yoke needs to be trued. The length of the yoke is what keeps the cylinder at the perfect position for each chamber. If the end of the yoke is worn unevenly, it will cause difficult opening at certain spots on the cylinder. Its a simple fix if that's the problem.

All advice is appreciated and I certainly won't remove any metal without a thorough investigation. Ended up traveling but when I'm home I will try all the suggested tests. Merl67 did you actually shorten the knob on the end of the ejector rod? How did you determine it was the culprit?