.Pixote. said:
The picture DB posted shows penetration, expansion, and wound cavity characteristics of assorted rounds of common ammunition in ballistic gelatin.
Most rounds designed to deal with humans and animals will deform at some point on or after impact. As the bullet deforms, it cuts a wider wound path and slows down considerably, imparting more of it's kinetic energy to the body as it travels. That imparting of energy is what makes the wound cavities you see.
The last one is a joke playing on the common myth of the raw destructive power of the 10mm. 10mm is very fast, containing a lot of energy. The picture is meant to imply that it will cause an explosion in anything it hits. 10mm also has a pretty stiff recoil. Plenty of folks hear about it and think that it is 'too powerful to shoot'. In reality, it's about as strong recoil wise as a snappy .40, and certainly no worse then many other calibers.
Finally, smaller bullets moving at higher speed tend to shatter or fragment on impact with bone, etc. You want a round that will deform (mushroom) at some point after it penetrates what you strike, and still have it travel deep enough to hit something vital. A different type of bullet, like a solid ball, doesn't tend to deform much, and is therefore more likely to travel right through the target, taking much of it's energy with it. A lighter bullet at higher speed might shatter on striking bone, dissipating much of it's energy at a shallow penetration. This is why most folks outside of the military use some flavor of 'hollow point' bullet, which will penetrate and expand.
Still fun to blow things apart with a musket from time to time! In fact, the only gun he has that is anything like the stuff in this thread is a Beretta g17, similar to the g19 + g20 that Ego posted a bit ago. 
