S&W K-frame trigger/hammer problem

Okay, I did a search and could not find anyone else with this problem.

Revolver is a Brinks trade-in M64-5 DAO (looks like it was made by S&W that way, but I'm not 100% on that). I bought it recently (used, obviously).

Sometimes, stroking the trigger does not cause the hammer to rise and fall. It moves just a very little bit, and that is all. Trigger moves through its full stroke, no jams or tough spots, although it does not feel as smooth as some. This only happens once in a while, so it's difficult to duplicate.

I took off the side plate, gently cleaned and lubed everything inside. Since then, I have only done some dry firing, and have not (yet) had the hammer fail to rise...but I'm not sure I fixed anything, because i did not find anything conclusive.

One thing I do note is that the trigger "stages" semi-normally, one click, two clicks, then the hammer falls. But the distance of trigger/hammer movement after the second click seems more than normal...and the effort after the second click seems to increase more than normal.

I don't have another DAO K-frame to compare to, so I'm comparing to my well-broken in, very smooth M-66 no-dash...may not be a valid comparison.

Any suggestions are welcomed.

Best regards, Rich

Thank you both.

I took off the side plate (again) and removed the hammer.
I also happen to have another K-frame (albeit not DAO), and did the same with it. I compared the length and the engagement faces of both, as well as the amount of force required to compress the spring acting on the DA sear. I also checked the amount of pressure exerted by the rebound slide spring, and checked to make sure both triggers are going fully forward.

I cannot discern any difference between the two.

I cannot swap them out, because one has the hammer-mounted firing pin and the other has a frame-mounted firing pin.

There is definitely a difference in the force required to reach full travel (greater on the that has experienced trouble). After having both side plates off, both revolvers are clean and well lubed inside, and it appears that everything that should move is moving relatively smoothly.

I was thinking of buying a standard hammer from Numrich (one with a hammer spur, complete with DA sear). Will this require a gunsmith's fitting?

Thanks again for your help.

Best regards, Rich

Update--and thank you again.

Okay, I'm not sure how I managed to miss this...but, the DAO M64 is a round butt, while the other is a square butt.
--The two strain screws are different lengths--is this a function of the round/square butt?
--The mainsprings have different curves to them as well.
--The "short" (round butt, DAO frame) strain screw is barely long enough to touch the "other" mainspring, while the "long" strain screw will clearly over-bend the (round butt, DAO) mainspring.

So now, everything is back where it began. If anything, I'm thinking I should buy a new standard mainspring and a new strain screw, and go from there.

Your thoughts?

4v50--

"Strain screw" is S&W's nomenclature, not mine.
I understand the function of the screw, and am only using correct terminology. Can we stay focused here, please?

Thank you.