A lighter bullet is usually constructed "not as tough" as the heavier bullet, hence it will expand or open easier and more rapid the faster it is pushed.
How would a slower heavier bullet cause more damage? Penetration should be taken out of consideration with.45 cal's on deer sized animal. I fail to see how a WFN of .451 or 2 will do more damage that a HP that has expanded to .750 or so at the same distance/velocity.
FYI, if a lighter bullet is not constructed as tough, getting the top speed (and the attendant pressures of the 454) is not a good thing. For example, you could use the Speer 250 Gold Dot HP, but it would need to be loaded slower both speed and pressure wise than its thick jacketed 300gr. counterpart.
Some bullets are designed for the 454's top speed pressures, others are not; bullet weight does not matter, since the ass of the bullet gets the pressure and needs to keep its shape, else pressures go nuts.
