Yes they bounce . In books on WWII that i have read, and being a tank Mech. M1A1, M88, M2A2,A3 sometime rounds would bounce off. most of the time they would just splatter. The book "Death Traps" is oputstanding story of a guys job to remove destroyed tanks form the battle fields in Europe. The Shermans/ most allied tanks muzzle velocity was so low it would splatter or bounce off the armor of the Germans tanks.
On the other hand I have hit a M-8 with a HE from 300 in a panzer and it bounced. Was'nt to happy cause he shot me an and i died. The GV needs some serious work.