Shape Memory Alloys (SMAs) are a special kind of active materials in which the martensitic transformation (MT) is the basis of the peculiar superelastic, and shape memory effects of great interest for technical applications.In a recent work, by studying a tensile stress-induced MT in a Ni-Fe(Co)-Ga crystal we discovered a new phenomenon consisting in unusual anhysteretic superelastic behaviour associated with a very large strain equal to about 14% at above a critical temperature value.With a diffraction experiment covering the full sample volume under stress, we would definitively clarify the microscopic mechanism responsible for the unusual superelastic behavior.The experiment will show if the model is valid for describing this unusual behaviour and will give a sound basis for applying this theory to similar alloys with applications in solid state refrigeration.