I think the 400 is a stopping cartridge on animals up to Buffalo but not on Rhino or Elephant.

To me, a stopping cartridge must kill instantaniously from any angle, not the perfect angle. Thus the 400 is too small for the pachyderms.

A 470 will usually do it and a 500 and up will always do it. This assumes the correct shot placement for the angle offered.

A stopping shot is not always a charge directed at the shooter. It is many times a charge directed at someone else at an unfavourable angle to the shooter.

But that's just my opinion.