Abstract: In one aspect, a firearm system allows multiple modular firearm configurations, thereby providing significant customizability of the firearm by the user. All of the components necessary to fire the weapon are carried on a common receiver assembly. Interchangeable slide assemblies and handgrip modules can be detachably connected to the common receiver to substitute one firearm size, handgrip circumference, and/or munitions caliber for another. For example, the handgrip module can be substituted so as to change the size of the firearm and/or the slide assembly can be changed for purposes of changing the caliber of the firearm. In another aspect, an improved firing pin safety, which is capable of use in a one-piece machined slide, and which is additionally capable of being manufactured as a stamped sheet metal part, is provided.