I suppose it’s possible that the firing pin was replaced. Check protrusion by opening cylinder and pushing hammer forward while trigger is pulled. Compare that to your other pistol. Also check your mainspring under the grips as people often fool with that. Make sure screw is tight and nothing has been inserted between spring and frame.
That’s about all you can do without help from a smith.
75% of the time a used S&W has misfire issues it's bc someone backed out the strain screw to get the DA pull weight down.
First check that the strain screw (which presses against the mainspring) is tight. Often people just loosen them and leave them. Even a 1/2 turn can make the difference between the gun firing and not.
If the strain screw is tight, but DA pull weight feels nice and smooth (ie low weight), either buy another strain screw, and buy a stock mainspring, and replace them. Strain screws are like $3 each, a mainspring might be $10
Edit: this is not a gunsmith job...it's an opportunity to get friendlier with your revolver. All it takes is a screwdriver.
