Mixed them up I have edited the post it should have read, "Pefectly elastic collision do not exist in the real world" the rest is correct
I hate to be the bearer of bad news, but almost everything in your post was incorrect, even after your edit. Throwing a lot of technical jargon at it to make it sound factual to a layman doesn't actually make it so:
Kinetic energy is not conserved in an elastic collision but energy is always conserved.
This is not correct.
Wikipedia page for Elastic Collisions said:
An
elastic collision is an encounter between two bodies in which the total
kinetic energy of the two bodies remains the same. In an ideal, perfectly elastic collision, there is no net conversion of kinetic energy into other forms such as heat, noise, or potential energy.
Georgia State University Hyper Physics page said:
A perfectly
elastic collision is defined as one in which there is no loss of
kinetic energy in the collision.
Then there's this:
All that kinetic energy gets converted/used/dispersed as tissues damage, plastic deformation of the bullet, hysteresis in elastic deformation, heat, vibrations, sound, etc.
This is the definition of an inelastic collision - an inelastic collision is one in which kinetic energy is lost, most typically lost as "plastic deformation of the bullet, heat, friction, vibrations, sound, etc":
Khan Academy Physics tutorial page said:
An inelastic collision is a collision in which there is a loss of kinetic energy. While momentum of the system is conserved in an inelastic collision, kinetic energy is not. This is because some kinetic energy had been transferred to something else. Thermal energy, sound energy, and material deformation are likely culprits.
And this:
Momentum is not really conserved any more than kinetic energy is.
Again, false. See above Khan Academy quote. Plus:
Georgia State University Hyper Physics Tutorial Page said:
Momentum is conserved in inelastic collisions, but one cannot track the kinetic energy through the collision since some of it is converted to other forms of energy.
And this:
If momentum was always conserved the bullet and target would never stop moving.
This is a gross mis-application of basic physics principles. You should know well enough, based on your subsequent statement copied below, the instant of the collision is independent of the momentum loss due to friction following the collision. During the collision, momentum is conserved, and then subsequently lost thereafter due to Newton's First law - an object in motion, or at rest, will remain at motion, or at rest, unless acted upon by an external force. In this case, the external force being friction. Technically, momentum isn't lost in that case, but rather, the target dragging against the Earth transfers an infinitesimally small velocity to the incredibly MASSIVE planet, with a net offset relatively similar, and opposite, to the velocity imparted by the frictional force against the shooter's feet when the bullet was fired... It's really not so complicated to follow.
Which concluded with actual science being misapplied to support a false conclusion:
The conservation of momentum in an inelastic collision is only conserved for that instant and only with the simplifying assumption friction is negligible for that instant.
This is the only factual part of your post, but your use of this evidence as non-conservation of momentum is false. Yes, during the inelastic collision, friction is typically ignored, therefore, the momentum the instant before is equal to the instant after, however, even when considering friction, momentum remains to be conserved - Friction is a mechanism for momentum transfer. In this case, the target dragging against the Earth imparts in infinitesimally small velocity on the relatively incredibly massive planet - a velocity which is technically offset by the friction between the shooter's feet against the Earth in the opposite direction when the shot was fired (and further extended to the air drag against the bullet in flight, as the resulting air velocity gradient approaches the static boundary layer effect at the surface - that far enough down the rabbit hole for you?). So in fact, Momentum remains to be conserved - it's simply transferred from the bullet, to the target, to the Earth. Just that simple.
So while the high velocity of the 357mag might yield Kinetic Energy numbers which look great on paper, it's really a misleading metric. The gap behind other magnum revolver cartridges is huge - hell, considering KE itself, the 44mag has greater KE at 100yrds than the 357mag at the muzzle. Let alone when you compare the more important metrics, like bullet weight, diameter, and momentum.
