As long as you (or previous owner) have not replaced or modified the OEM rebound spring (using a lighter one), I would expect the SA bevel on the trigger needs to be sharpened. Another possibility would be dirt, shooting debris, or old lubricants compromising the action itself. These contact points are susceptible to wear just like any other interface. If the rebound spring has been lightened, or a lighter spring used, going back to the OEM spring may cure the problem.

What is the SA pull weight now?

Sharpening the trigger bevel is a very simple job, but requires the correct stone and the use of the correct procedure. As long as there is no significant damage, a trained, competent gunsmith qualified to work on revolvers should be able to fix the problem without replacement of any of the components.

The other viable option would be to call S&W Customer Service and send the gun to be serviced. While it's there, you could have them check the gun over to be sure it meets specs. 1-800-331-0852

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Ret. LE, FA Instr, S&W Armorer