On 1942-10-10, the muzzle velocity for Shot, AP, capped, M51 was changed to 880 m/s (2 900 ft/s).
Sources
TM 9-1250
Muzzle velocity
Shot, fixed, AP, capped, M51
780 m/s (2 550 ft/s)1
Shot, fixed, HE, Mk. II
820 m/s (2 700 ft/s)
Shot, fixed, HE, M63
810 m/s (2 650 ft/s)
Sources
War Department. Technical Manual, Ordnance Maintenance : 37-mm Gun Matèriel (Tank) M5 and M6. Washington : War Department, 1942. 1942-03-10 version, with ammendments from 1942-11-06 and 1942-10-10. TM 9-1250.