Claim: 75mm L/31 (M2) guns have lower muzzle velocity compare to guns classified as 75mm L/40 (M3/M6).
Evidence: The US 75 mm gun was the standard American gun mounted to a mobile platform during World War II. 75mm L/31 (M2) 563 m/s (1,850 ft/s) 75mm L/40 (M3/M6) 618 m/s (2,030 ft/s)