I've used 300 grain 9.3mm jacketed bullets of several brands in a .400/.360 at 2000 fps for many years and have never had a problem with inadequate expansion. What kind of bullet were you using? A 250 grain Woodleigh RNSN at the standard 2250 fps from a .358 sounds ideal to me.

The ballistics of the .318 Westley Richards (actual, not table; one of the few British cartridges that consistently fell short of advertised velocity) is virtually identical with 250 grain bullets, and it was considered a great killer.