Flash suppressors having novel expansion features are disclosed. In one embodiment, a suppressor apparatus includes an attachment portion adapted to attach to a gun barrel, and a suppressor portion coupled to the attachment portion. The suppressor portion has a suppressor bore therethrough that is adapted to be aligned with a longitudinal axis of the gun barrel to allow a projectile from the gun barrel to pass therethrough. The suppressor bore is defined by at least one bore surface having at least one expansion groove disposed therein. The expansion groove may be partially-circumferentially disposed about the suppressor bore, or may include a plurality of expansion grooves. In another embodiment, a flash apparatus includes a suppressor portion having a plurality of longitudinally elongated members spaced apart about a circumference of the suppressor bore, each elongated member being separated from adjacent elongated members by a longitudinal slot, at least one longitudinal slot having non-parallel sidewalls.