Abstract: A firearm is provided having a firing pin block which pulls the firing pin away from the hammer independently of the hammer actuator mechanism. A loaded chamber indicator includes a pivoting indicator lever resistant to breakage and jamming. The firearm also has a reversible thumb safety which is readily inserted, releasably retained and fully operational in either side of the firearm. An ambidextrous thumb safety includes two shaft portions each having integral levers and adapted to mate together to form a single shaft. A selective magazine catch is also provided which allows the shooter to select between a magazine catch mode and a magazine free fall mode.