1. An ammunition cartridge comprising: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 propellent 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.