[3] The weapon itself was largely based on the American .50-caliber (12.7 mm) M2 Browning heavy machine gun, while the design of its ammunition was initially based on various Italian Breda-SAFAT 12.7 mm rounds.[1] The Ho-103 achieved a slightly higher rate of fire (RoF) than the contemporary aircraft-mounted M2 Browning machine gun (AN/M2) by using the smaller, lower velocity semi-rimmed Breda-SAFAT 12.7 mm cartridge.To compensate for the mild to moderate loss in performance, the gun was frequently loaded with high-explosive incendiary (HEI) rounds.[1] The 12.7×81mm cartridge allowed the Type 1 to fire at a rate of 900 RPM, but the poor suitability of the Browning's action to synchronization reduced the rate of fire to 400 RPM in synchronized installations.[1] However, the Japanese source and Allied Intelligence reports[7] did not mention that this machine gun had a propeller synchronization flaw.
Some examples of Ho-103 cartridges. From left to right: AP-T (red tracer), AP-T (white tracer), Ma 103 HEI (two-piece fuze, traces of white seal are still present in the knurles on the projectile), Ma 102 HEI.
