Stoppage-inducing ammunition cartridges have a case having a rear head surface, a circumferential extractor groove forward of the rear head surface, a body portion forward of the circumferential extractor groove defining a case axis perpendicular to the rear head surface, and a forward mouth, a primer received in the case, a propellant within the case, a bullet received in the forward mouth, and the circumferential extractor groove being defined in part by a rear extractor surface angularly disposed with respect to a plane perpendicular to the case axis, such that an extractor adapted to engage a groove surface perpendicular to the case axis will have limited effect at extracting the cartridge from a firearm chamber after discharge. The rear extractor surface may be a frustoconical surface. The rear extractor surface may be a tapered surface acutely angled with respect to the case axis.