Description is given of a set‐up for the determination of temperatures at the frictional interface between a moving bullet and the bore in a caliber 0.50 gun barrel. Cathode‐ray oscilloscope e.m.f.‐time records, which were obtained from a traveling thermocouple junction formed by the bullet‐bore interface, are interpreted (by use of a formula due to Jaeger) in terms of instantaneous temperatures. A calorimetrically measured value of the total frictional heat input caused by a bullet being pushed through a barrel section by means of a falling weight, is found to be in good agreement with the value of the heat input calculated from bore surface temperatures which were determined by the sliding thermocouple method.