All things being new and untouched, the primary regulator in this relationship is the bevel on the trigger. It's sharpness and angle are critical.....pressure exterted from the mainspring and rebound also play an important roll. I agree with Tomcatt. IMO, the pressure/tension supplied by the rebound is more important with respect to SA than the hammer tension. Slight variables in the manufacturing, fitting and assembly process make each gun unique though.....especially the older, "pre-CNC" models.

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Ret. LE, FA Instr, S&W Armorer