Model 65-1, new to me, has an incredibly light single action trigger pull...scarey light. Did a push test of hammer and it dropped with little pressure of my thumb. Haven't disassemble yet as I'd rather hear from someone with expert knowledge to hold my hand by telling me what in all likelihood is the problem, what I should be looking for in terms of worn parts, accessibility of replacement parts, or should I just locate a competent gunsmith or ship it to S&W?

Commonly called "push off", the condition is usually the result of modification or damage (wear) to the SA bevel on the trigger, or the cocking notch in the hammer. The S&W armorer's manual describes the forward thumb pressure used on the hammer spur when testing as "moderate". To me, that's around 5lbs of forward pressure on my gauge......but it's still a "judgement call" as to what moderate pressure is. Remember that any SA hammer will fail this test if too much pressure is exerted, and that improperly forcing the components can actually damage the hammer and trigger interface.

If you are capable, do a good cleaning and lubrication of the interior and parts. Check the bevel on the trigger and the hammer's cocking notch with a magnifier after cleaning. You may see evidence of damage or improper modification. (stoning)
If you purchased the gun used, it's possible that a previous owner has modified the action by installing a lighter rebound spring, cutting coils on the OEM rebound spring......or by backing out/shortening the mainspring strain screw. This can often make the "push off" condition worse. Sometimes, installing a new, OEM rebound spring can help resolve or mitigate the problem.

If re-installing a new rebound spring doesn't help, or you see damage on the trigger bevel or hammer, you should seek the help of a qualified, trained local gunsmith, or call S&W Customer Service. The bevel of the original, used trigger can usually be restored to proper function by stoning to the proper factory angle/edge as long as it hasn't been damaged beyond repair by improper stoning or other modification. If the hammer is damaged it cannot be repaired, it will need to be replaced.

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Ret. LE, FA Instr, S&W Armorer

Armorer951 -
I thank you for your advice. Tonight or tomorrow morning, I'll disassemble for a thorough cleaning and close inspection of internals. I'm comfortable replacing springs, but beyond that I'd leave it to an expert. Hope you'll check this thread again as I'll post the results of inspection and, may very well need additional sound advice/guidance. Thanks again!

Feedback about the repair process is always helpful to others here on the forum. Thanks in advance for posting your experience and end results.

The repair of a "salvageable" SA trigger bevel is a simple, straightforward 30 minute job, but does require training and specific tools.

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Ret. LE, FA Instr, S&W Armorer

You always get great advice from armorer951
I purchased a gun that had push off and was able to correct it with the correct tools. However I experienced the situation later with another gun that I felt more confident letting a gunsmith correct it

As a personal input I think you would benefit in the long run to have an armorer or complete gunsmith give it a complete servicing so that you have confidence in the gun and safety in place. It is possible too that when the gun is opened up that someone may have also removed the hammer block assembly.

It is possible I think that the mainspring could also be getting a bind from the trigger rebound return spring housing and not allowing it to go in a full cock position if someone has improperly bent the mainspring to lighten the action. I've seen this too.

Certainly keep us up to date, everyone learns from it!
Karl

What tools restore a 0.005 in deep SA sear notch? I would never fool with this, but am curious how a competent pistolsmith would get the notch not only the correct depth and profile, but true, square and parallel across the span of the hammer. Seems a little risky to remove case hardened surface metal, or is the work done before case hardening?

The damage in this case is to the trigger bevel, not to the hammer notch. If you read the posts I specifically told the OP if the hammer notch was damaged it could not be restored, and would need to be replaced.

You are correct in your assessment of re-cutting the hammer notch. This could not be done with hand tools, and would require a high quality milling machine. After re-cutting, the restored notch would have to be re-hardened. It would therefore, be much more cost effective, to fit a new hammer.

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Ret. LE, FA Instr, S&W Armorer