The reason your woodchuck stays where it is is because the bullet doesn' t actually ' hit' it, it goes through it, were the entire energy of the bullet transferred into the woodchuck at the same instant, then your WC' s going a LONG way, but it' s easier for the skin to rupture and organs to explode than to move the entire animal. One of my physics professors took us out to the Union square to demonstrate this one, he took his truck, an egg, and a football, had one of us drive at 35mph, then tossed the egg up in-front of the truck as it drove by, the egg splattered, longest spray was 6.5ft, then he took the football, and did it again, could have been a record field goal, it held intact. When a bullet hits something, it' s like the egg, it ruptures, and energy is wasted, whereas if the two objects reacted like billiard balls, a " perfectly" elastic collision following which both object move on at 100% present mass and condition (i.e. no new dents that would have acted like cushions, increasing the period of time over which the impact occurs, ever heard of collision cushion quarter panels?). Basically the bullet never really ' hits' anything (bone excluded, which hardly counts because it only acts as an instantaneous cushion), it changes between media, it can travel relatively easily through air, but when it enters the ' water' of the body, it slows down greatly, it' s kind of like a collision, but it' s buffered, the skin holds together a bit more than air, and the meat/organs do a little less, but they still let the bullet travel through, slowing it, not instantaneously stopping it.

If you shoot something hard, like a boulder, giving a billiard type rebound, it is possible that you could move it slightly, but then a system of frictions come into play. Ever notice how it is a whole lot easier to move something once you get it moving or rolling? These frictions are called static friction, rolling friction, and sliding friction. When you push on a box on the floor, everything is stuck together like velcro basically=static friction, once you get it moving, it doesn' t have time to rebond as well and the inertia of the box helps you move it, but friction is still present=sliding friction. When you start pushing your truck, it doesn' t want to move=static friction, once it gets rolling, the inertia of the truck helps you, and it becomes much easier=rolling friction...even the inertia of the wheels rolling aids you...that' s why you don' t usually see boulders shift at all when you ricochet a .22lr round off of them, it' s much easier to restart the bullet in the opposite direction against virtually nill friction, only that of air resistance, than to start the boulder moving against the ground, even if it isn' t sunk in a foot or two. Not to mention that your bullet ' expands' , acting as a cushion.

Physicists LOVE billiard balls and ice, the above is why.