Welcome to the forums from the Wiregrass! Go to an auto parts or hardware store and get some aerosol brake/carb/parts cleaner. Flush the action through the hammer or trigger openings until the effluent runs clear. See if that restores the single action. If not, you may need to have a gunsmith look at it. Be sure to lube it afterwards with 5 drops of gun oil into the action from the hammer or trigger openings.

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Guy
SWHF #474 SWCA LM#2629