the gun on the panzer IV had 385 m/s muzzle velocity firing a 6.8 kg shell.
the L-10 on the t-28 had 555 m/s muzzle velocity and fired 6.3 kg shell .
the kinetic energy = 954.8 KJoules for l-10
ke= 503.9 KJoules for kvk-37 .
the gun on the t-28 is almost twice as powerful as the gun on the early panzer iv, and all data i had sean gives it comparable penetration with the L-11 mounted on KV-1.
even in a b1 bis vs pz-IVd setup, the french tank was not immune to shots in the tracks or the radiator.