Faust is a one hit kill on sides and rear of any allied tank cept the Churchill, and the Achilles, and the Achilles is only due to the current bug where it has about 3000 hit points, when it should only have around 500.... If you hit the track/sandbag armour, it functions the same as the schurzen on the Panzer 4. Now, if you hit an unprotected sherman, and it still didn't die, then that's probably more due to server lag then the faust not actually killing.