It is shown that crystals with the symmetry m 3 and m 3m are suitable materials to study if one is seeking to detect the dependence of electrogyration on stress which is described by an axial tensor of rank five. Experiments are performed on methylammonium alums doped with chromium. Several properties of the material enable critical checks of experimental results to be made. The checks are needed because the intrinsic effect is usually smaller than effects which are caused by the interaction of linear and circular optical properties but which are no signature of intrinsic piezo-electrogyration. At room temperature a stress-induced electrogyration of 6 × 10^-17 V^-1 Pa^-1 has been observed. At a temperature of 200 K which is 25 K above the transition into the ferroelectric phase the magnitude of the stress-induced circular electrodichroism is 10^-15 V^-1 Pa^-1 in a sample with 10% chromium. These magnitudes are considered to represent upper limits of piezo-electrogyration in crystals because they result from special properties of the doped alum.