I've started modding Left 4 Dead 2 a little. Changing the rate of fire for many of the guns. When I do that the guns really become more respectable.
For example. The AK47 in the original game fires 461 Rounds per minute. In reality it would fire 600 rounds per minute.
In the game the Mac-10 would fire 960 RPM while in real life it would fire 1135 RPM.
Personally I don't approve of them changing realistic weapons so that they act differently in the game.
And I can hear the cry of the fan-boys saying: "But Kent - realism ruins the gameplay in games!" Bullshit, I can play just fine with only 30 bullets in my clip and realistic values in the fire-rate, damage and penetration. Hell, I'll even let you try playing with my realism mod.
For example: The AK47 will pass through many common infected but wont do that much damage against them.
The M16A2 will do alot of damage against common infected but wont pass through targets. It will also inherit the burst ability that the SCAR initially had.
The SCAR-L will behave in much the same way the M16A2 would except it doesn't burst.
The desert Eagle should not leave such graphic wounds anymore but will still kill every common infected.
The Uzi should fire slower and be much more accurate.
The Mac-10 should fire faster but be less accurate.
Don't ask me about the shotguns. I'm going to improve their spread and damage so that infected will be more susceptible to their effects. The problem in the shotguns is that they're not modelled after real shotguns (or at least not any especially known models). The Pump shotgun looks like any american pump shotgun. The Chrome is a little more interesting but is also a largely unknown brand. From what I can gather from the L4D2 wiki these guns are Remingtons. At least Chrome is, the pump shotty alá Left 4 Dead 1 is a mix of different brands.