Originally Posted by MLeake
Most projectiles have a velocity range below which, they will not expand, and above which, they fragment - potentially preventing penetration. (Alliteration free of charge.)
So one could argue velocity is more important with regard to finding the ideal velocity for the particular firearm and bullet combo.
I think we're getting beyond galoshes here and getting into hip boots territory, but try this: It isn't a bullet's velocity per se
that causes expansion, it's the energy driving the bullet into the medium. It's not really possible in the real world, but it could be computer modeled: Suppose you could take two projectiles of the exact same shape and profile -- say, a .45 caliber, 230-grain Golden Saber bullet. One of the two IS a 230-grain Golden Saber bullet. The other doesn't use lead as a core but instead is made of some alloy of Unobtanium, that has zero mass. So projectile number two has the same jacket, the same open nose, the same cavity ... but the "stuff" inside weighs nothing so the total projectile weight is not 230 grains but perhaps 30 grains. (?)
Now accelerate both to the exact same velocity and let each one impact your test medium of choice: ballistic gelatin, wet newsprint, hog carcass, your mother-in-law ... whatever you choose. I respectfully submit that the second projectile -- the one filled with a core made up of weightless Unobtanium -- will not expand nearly as reliably as the standard Golden Saber projectile.
Why? Because it requires energy to expand metal, and both lead and copper are metals. It is hydrostatic pressure of the impacted medium that presses into the cavity to force the bullet to expand, but the impact medium is static. It has no kinetic energy, so where does the energy come from? It comes from the energy -- the momentum -- of the projectile. Yes, it requires velocity, but it also requires mass -- and the question posed at the start of this discussion ignored mass. ALL we were asked about was velocity or energy. Projectile number two in my hypothetical experiment will have FAR less energy than the standard bullet, at the same velocity.
When those are the only two options, the only valid choice is energy.