This one will ruffle some feathers.

Hyrdoshock is the culprit.

I've seen some huge entrance holes on game as well when soft bullets were used, much larger than the exits.

Interesting thing about this photo is the fact that the bullet didn't expand. Imagine the same photo w/ a Vmax (That is if there was and apple left to photo )

Reloader

This photo is not the final result it is a shot of the continuing reaction.

The difference in the hole sizes are due to the fact that the entry hole has had more time to expand because the bullet hit that side first.

In later frames of this motion picture the exit hole will expand more and the entire apple will probably disappear with the violence of the reaction.

There have been some unpleasant court cases where less than competant forensics people who have claimed 'he was shot in the back' because that's where the smaller hole was !I had two dramatic examples with 300 gr 45-70 where the entrance hole was 2" and the exit 1" diameter .the holes all looked like they were cut with a cookie cutter !! There are many factors involved .

I'm with Fjold.
- mike

I'm with Fjold too! Newton's third law is at work here. Force applied by the bullet strike compressed the apple somewhat before bullet entry, and with said apple pushing back, the entry is larger than the exit simply because it is an older wound. The exit wound will become larger because of momentum(the bullet setting the apple's innards in motion), and because there will be the secondary force of the apple trying to draw itself back. It is at this point where hydrostatic force will cause the apple to explode when the total sum of force(s) applied, exceeds the elastic strength holding it together.

If the animal is of sufficient size it is very possible that the velocity difference would explain it. Fast bullet upon entrance, slow(er) bullet at exit.

Throw in an expanding bullet and where the bullet is in terms of it's state of expansion would probably override the velocity factor alone. (grossly oversimplified I know)

I also agree that on the apple above the fact that the entrance hole has been expanding longer is the overriding factor.

quote:

Originally posted by Fjold:
In later frames of this motion picture the exit hole will expand more and the entire apple will probably disappear with the violence of the reaction.

I think you will find that this is a single exposure, not a movie.
Dr Herald Edgerton (MIT professor at large and inventer of the strobe light) would have it no other way. It is taken in a dark room, with a open shutter and a single strobe pulse.

Here is another one he took,

I have personally observed the larger entrance hole on an aluminum target. A friend & myself took some 1" thick aluminum slugs from a project at work & shot them with a 308 using military issue FMJ ammo. The entry hole was larger. I believe that while the target material was "in motion" it acted more upon the entry hole than the exit hole.
Where did you come across that picture? It looks like the album cover from an 80's heavy metal band "The Bullet Boys".