"With these loads (Modern 45-70 lever action, Speer 400 gr flat point) is powerful enough for any North American game except the large bears as long as the shots aren't too long. The construction of the 400 grain bullet is not tough enough to penetrate properly on large bears."
Speer Reloading Manual # 13 pg 414.
I would think that would be the final word on this from the bullet's manufacturer.
