A firearm with safety mechanism in one embodiment includes a barrel supported by a housing, at least one cartridge-receiving chamber in communication with a bore of the barrel, and a rotatable hammer. The safety mechanism includes a biased safety component, which may be a blocking pin in one embodiment, mounted to and rotatable with the hammer. When the firearm is exposed to an abnormal impact force caused by bumping or dropping the firearm, the safety component changes position and interacts with a blocking feature on the hammer pivot pin to stop or delay the motion of the hammer in a manner which prevents discharging the firearm. The blocking feature may be a notch in one embodiment. Rotating the hammer between rearward cocked and forward firing positions alternatingly aligns or misaligns the blocking pin with the notch, respectively.