James, when you process game killed by a hard cast flat nose, have you found evidence of tumbling?

No, In fact the strong point of wide flat nose is that they do not tumble after impact therefore they continue to penetrate better. A bullet that deforms in any way will start loosing penetration. That said, If the rate of twist is wrong in your barrel, they may tumble before impact. If they shoot well and don't show signs of tumbling on a target, then they should not tumble on impact with a critter. Pentration depends somewhat on the bullet continuing on the straightest possible path. Deformation will almost always cause a bullet to change its path. Thus a cast bullet should be hard enough to maintain its shape but soft enough not to shatter on impact with big bones or tough hides. The study of alloys can take a life time. I cast some bullets but prefer to purchase them already cast.