Steel does NOT penetrate nor carry it's velocity nearly as well as lead.
That is the reason waterfowlers up their shot size for ducks & geese when they have to use mandated steel shot.
I have used 000 lead shot (.360 diameter), Foster slugs and Brenneke slugs on bears.
The shot did not penetrate well at all. Stopped upon meeting bone at close range. Pass.
The Foster's penetrated better, but not nearly enough for my liking.
The Brenneke's penetrated the best - often a pass through.
Try the test out noted by Brutus above.
He may be somewhat off target when it comes to voltage in salt water, but in this case he is bang on.
Cheers