One of the concepts that has grown out of the small bore, high velocity era of firearms development is that low velocities rendersmall bullets fairly ineffective. The modern projectiles need significant speed to make a clean kill. At higher impact velocities, a bullet is capable of making a wound channel many times larger than its frontal diameter.

The large bullets of yesteryear don't need that much speed to be lethal. About the only thing extra speed gives you is a flatter trajectory, at the expense of increased recoil of course.