Tough Life Weapon Mod
Just extract the weaponinfo.xml on your GTAIV/common/data folder. Remember to backup your file, and applying the "magic" patch!
This mod is tough, and intended for people who like realism, tactical shooters, or even a challenge. You'll have to take cover always on firefights, and aim your shots, because with 6 mags per gun and enhanced damage, every bullet counts!
Use short bursts or even fire single shots. For tough missions (like the stripclub assassination) wear a vest, always. Avoid useless fights. Get em' Tiger.
As for the physics, now people will be genlty pushed as bullets just GO THROUGH (except for shotguns, ofcourse) and do not push you back! Stopping power is present only on armored enemies, but sadly, the engine makes no difference, so I prefered it this way, as most of the people you'll kill will be unarmored.
Images inside the arhive.