I saw exact same results a few years ago. Misfires, jammed hammer, etc. Someone (no one would fess up, a mystery of life) had run out the strain screw to the point the mainspring jammed the hammer when cocked. Locked it up like described. Before that was getting light hits and misfires. There was absolutely no need to bang on the cylinder. Absolutely no reason. Remove the side plate and easy fix.

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183rd FBINA