VP - I thought that part of the reason for the large exit wound was to do with the spinning of the bullet and the way it caught up the insides as it went through.
However, I've never fired a bullet at a tim or a proddy, just what I picked up someplace along the line.
Hmm, some explanation needed.
All modern forearms except shotguns have a rifled bore (look down the barrel and you'll see twisting lands and grooves) this imparts spin along the central longitudinal axis of the bullet and helps it retain accuracy in flight. This does not cause an enlarged exit wound.
Some firearms, most notoriously the M16 assault rifle, use a round that can, in some conditions, "tumble", i.e. spin along its' longitudinal axis, but also wobble as gravity and friction lessen it's ability to spin along the longitudinal axis. If this happens, you have large entry and exit wounds.
In terms of the penetrative and damage-doing qualities of different types of rounds, a "lead" (usually an alloy containing lead and other metals, not pure Pb) round will enter the body cleanly, but will break up on impact with any solid mass such as bone, and the fragments can be either widely deflected, resulting in you having bits of bullet lodged in you, or exiting you at widely-differing points, or can be narrowly-deflected and exit you
en masse at a broad focal point, leaving a crater where your flesh used to be.
Fully-jacketed rounds (as used by regular military forces and many police forces) make clean entry wounds, smash through bone and organs, but leave relatively (and bear that word in mind) tidy exit wounds.
The real bastards are jacketed hollow point rounds, which have all the penetrative abilities of a fully-jacketed round, but with the added nastiness of the "mushroom" effect caused by the lead alloy core of the bullet being accelerated and starting to leave the metal jacket as soon as the bullet hits the target
