[ETD]

Sorry, to be a wee bit slow, but...
Big Z, in your photo's, the magnums were NOT "bigger" but longer and all but the .22 had the metallic cap so that to a novice, those were the differences NOT the overwhelming size difference as in your photo's of the drinking containers. Or was that because of the loss of perspective in the photo's of the bullets and there IS really that much difference in size.
Paragon, that's what I was wondering. That is, the difference in projectile effectiveness has to do with the fact that there is that much more explosive material in the magnum bullets and not that they are longer and capped with some other metal (i.e. they needed to be longer to be able to hold more explosive force).
BTW, I figured that if shape was of primary importance, wouldn't bullets still be spherical? Doesn't a sphere going forward in air have the least drag coefficient or is my physics too rusty?