rybohunter, one important thing to keep in mind when considering different cartridges is their taylor factor...the .243 carries more energy, but it's also got a considerably smaller and lighter bullet...the energy transfer is more rapid (regardless of the bullet's velocity), both of them are capable of creating a hydrostatic shockwave, however, the bigger the bullet, the bigger the wave it can initiate with the same velocity...

I.e. jump into a pool off a 5' dive, do a cannon ball, you're a great big bullet not going very fast (relatively), you get a great big wave that can travel a long way before dissipating, now jump off a 10' dive and dive in, you're a small bullet going much faster, even if you spread your legs and arms as much as you can upon impact, you're not going to get much of a wave...the initial wave is what counts, transfer of energy, not raw energy.

Raw energy provided mostly bullet weight doesn't dissipate as quickly when a medium change occurs, i.e. a heavy bullet doesn't lose as much energy when it changes from a light medium (air) to a dense medium (liquid-which living tissue tends to act like in a "physics" sense), Even photons (light) change velocity when changing medium (ever been spear fishing).

The taylor factor on the .30-30 isn't huge, but it's certainly more than on the .243, and the dependance of energy on bullet weight is much greater than that of the .243.

Kinetic energy=1/2(mass)(velocity)^2, one half mass times velocity squared, so if you cut your velocity in half, you reduce your energy to one quarter, if you reduce your mass by half, your energy only cuts in half...so if your mass contribution is more prominent, your velocity changes won't matter much, whereas if your mass is small and your energy is mostly dependant on velocity, when your bullet slows down, it sheds a LOT of energy.