ISU-152 is the worst tankkiller #1 ingame. with ISU-152 HE ammo you can kill all tanks till jagdpanther, pershing, tiger, centurion .... frontaly without any problems (useing max. range).
killing ISU-152 frontaly needs >100mm penetration -> at this distance ISU-152 can kill most tanks frontaly with HE or AP.
sometimes i saw ISU-152 or KV-2 killed KTs frontaly with HE -> HE hit turret from KT -> KT lost whole turret. LOL
same with HE from IS-2 or IS-3 against tiger/panther/pershing. HE hit turret -> tank lost whole turret.