Hypothetical..

Two hardcast, gas checked bullets for .45-70. Let's say one weighs 425 grains and the other is 575 grains.Designs are as identical as can be with the weight difference.Both loaded warm, but under Max.

Alaskan moose and possibly large bears.
What (if any) would be the advatage of the heavier bullet?

Being a 45-70 shooter and just in the 405 cast I would think the only advantage would be deeper penitration if bone was hit, but I am no expert. I also think in a quartering shot the 425 would be more than enough, even enough!! But I have no game experience with the cast on those large animals, just what I have read about there performance.

Bob, Thanks kinda where I'm going with this!
How much weight is Enough, and when does it become "overkill."

Over kill is not a bad thing with bad bears, like a bush pilot flying us out once off of a lake, he taxied all the way to the down wind side, [bleep] we taxied for 10 minutes at least, yes I know you take off into the wind, I asked him why so freaken far, "because if I need more room to clear the trees, I cant go back and get it"!! Good point, and well taken.

Read the Sandyhook tests on the .45-70, they will go into the penetration differences between the 405 and 500 grain bullets of that era.

I have loaded both the 420 and 540 grain bullets, but I really can't tell you if one will out-penetrate the other. I've never recovered one of either weight.

I've run the 420s at 1650 fps and the 540s at 1550 fps, and to be honest, I feel that the 420s at 1650 are medicine enough for this continent.