Left 4 Dead
Left 4 Dead is a singleplayer and multiplayer cooperative survival horror FPS game.
Know Your Modding - Replacing a Gun
Finding a Model
First you will need to find a model that you want to replace with. In this tutorial I'm going to replace Hunting Rifle with Maverick-A2 from Call of Duty.
Tools that you'll need.
3ds Max or Blender (I use 3ds Max 2012)
Notepad ++
Left 4 Dead
SMD Importer and SMD Exporter plugin for 3ds Max/Blender.
Getting started.
First I usually make a folder where I put models/materials. (like in the picture)
After you decompiled the model, you will get a smd file and the qc file.
Now decompile the original model
3ds Max
If you have 3ds Max, once you open it, it will look like this
In the left upper corner click this button 
and then click on import and find the smd file for your replacement model.
After you imported all models that you need, it will look like this
Now try to match the replacement model with original model as best you can (as in the picture)
Adding weight to the new model.
After you matched the replacement model to the original model, click on this and find Skin Wrap(make sure the replacement model is selected, not the original model)
After you added Skin Wrap, first press Add and then click on Original Model (it should freeze for a bit)
Once the 3ds max unfreezes, tick "Weight All Points" and press Convert To Skin.
Finishing Touches.
Once you Converted Skin to the replacement model, delete the original model because you don't need it anymore.
Now you will need to edit weight because It's not perfect. We use this tool for this
I use this thing called "Element" to hide parts of the model so it makes the job easier.
Once you start fixing weights, make sure "Vertices" is ticked
with the left mouse, hover the model like this
so it looks like this
Now go to the "Weight Tool" that we mentioned earlier. 
Once you open it, click on the bone and press 1
Once you did it, part should look like this  
Now go back to the Element and press "Unhide all"
Do the same thing for the trigger
When you're done it should look like this
Export it now.
Export the model as smd file and compile it.
You're done!
congrats! you made a weapon replacement!
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What people are saying...
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Kalu August 2017
G Job
M5_Prodigy February 2017
Im lost badly i dont even know to import im such a beginner.
Knuxfan24 October 2016
So I'm probably just missing something, but I cannot get View Models to work for the life of me. World Models are fine, but View Models don't animate & have the character's arm stretched to what I presume is the map's 0,0,0 coordinate.
ivanardian January 2017
me too, i'm not creating my own weapon, i just want to port rifles mod from l4d2 to l4d but i can only get the world model working and yes the view model doesn't work even the survivors arm become strecth and twisted. Any help about it?
emanbees September 2016
Good Job bro!!!