I shot a hand cast T/C Maxi Hunter style bullet weighing 333 gr with 80 gr FFg, got 36 inches of penetration. (head on shot at 50 yards or so) deformed nicely in the nose. Still weighed 300 grs or more (can't remember now...)
I just tested my 50 cal 180 gr PRB with 80 gr FFg at 20 yards and gallon milk jugs of water. The first two jugs were really destroyed and the RB was collected in the 8th one! No deformation apparent...