Momentum vs. Energy...:
Lets say we have two calibers
(numbers chosen for simple calculation)
1. a 'Solid' with m = 20g and v= 500m/s
2. a 'Solid' with m = 15g and v= 1000m/s
For simplicity we assume that both bullets have same diameter and will not deform in target...
We now shoot both calibers at a target in which 1. will stop on the far side skin, which means that it will loose all momentum and energy to the target.
2. will ofcourse produce exit wound and will fly on, loosing only part of its momentum and energy to the target... lets say it will exit with 700m/s...
Now we add up momentum and energy:
Before target
1. has 10Ns momentum and 2500J energy
2. has 15Ns momentum and 7500J energy
After target
1. has 0Ns and 0J
2. has 10,5Ns and 3675J
Because momentum and energy are lost to the target we get for
1. 10Ns and 2500J lost in target...
2. 4,5Ns and 3825J lost in target...
(btw to just get the same momentum lost to target 2. has to be slowed down to 333m/s... on the way it will loose 6670J to the target...)
With some common sense and practical experience one would say that 2. will make the most damage by far and kill better...
This is true for the energy lost to target - 2. lost 1325J more to the target...
It is completly false for momentum because 1. lost more than double (5,5Ns more) to the target and if momentum would mean damage to target it would mean that the wounds of 1. would be much server (double?) than of 2. ...
The trick with the better 'killing power' of the slow/heavy bullet compared to the fast/light bullet is, that the mass will penetrated deeper into the target and can reach the area were it most hurts, while the small bullet will not penetrated as deep because its deformation and mass will not allow it...
Its energy is lost where it is not so lethal...
But if you take a say .500SW which kills a bull better than a .243 because of penetration a .50BMG will kill it even better even when it not lost as much momentum as the .500SW... the total energy lost to the target will be (very) higher... resulting in server wounding...
And when momentum could kill a deer it would kill the shooter before the deer because the shooter gets hit by the same momentum as the deer through the recoil...
Actualy he gets even more momentum than the deer...
For one the bullet will loose momentum in flight to target and while the rifle will be completly stopped by the shooter (transfer all momentum to shoot) the bullet will exit the deer taking with it not lost momentum...
Velocity and bullet typ is all you need...
And while you can always go up in speed you can not have the super expanding super penetrator (yet)... You will allways have to choose the right kind of bullet for the target and speed...