(Step 0) Have 7-zip or Winrar installed. I'm using 7-zip; hopefully Winrar is similar enough to make this guide work for both.

(Step 1) Navigate to the DOOM 3 file directory. For the Steam version, go to the DOOM 3 listing in your Steam library, right-click on the game, and go to Manage --> Browse local files. Alternatively, find your main Steam directory, go to steamapps --> common --> Doom 3. Your Steam directory is probably just called "Steam"; mine is "SteamLibrary" because I have the primary Steam folder on my C: drive and most of my games on my E: drive.



(Step 2) Go to the "base" folder and find the pak00X.pk4 files (X being any number). You'll jump between pak000 and pak006.



(Step 3) Open pak000.pk4 with 7-zip. Note the "def" and "script" folders--these are the folders in each pk4 we'll be looking at.



(Step 4) Go into "def" and find "weapon_shotgun.def". Right-click on the file and click "Edit" (or hit F4). Notepad will pop up (or your preferred .txt editor--I'm using Sublime Text) containing some of the code for the weapon.



Scroll down a little and find the "spread" variable. If I remember correctly, the default value is 22 (Why, id?). You can change the value to whatever you want; I set it to 6 because that makes it so that it's a short-range weapon rather than a melee weapon.



Save the file and close out of Notepad (or whatever program you use). Make sure you get a prompt asking you to update the file you just modified, and say "OK".



(Step 5) With less spread, the shotgun will be kind of overpowered now. If you want to make it less OP, you've got two options: decrease the damage in same "def" file that you just modified, or change the number of projectiles the shotgun fires.

To do the second one, DO NOT go to the "script" folder in pak000. The pak files are loaded up sequentially, and there are duplicates of the weapon code files in the later paks that overwrite whatever was loaded from the previous pak.

Instead, go to pak006. Go to the "script" folder here and edit weapon_shotgun.script. Towards the top, you'll find SHOTGUN_NUMPROJECTILES. It's default is 13, if I remember correctly; I changed it to 10. Save, close, and make sure it gets updated in the archive.



I will say that reducing the number of projectiles makes the shotgun less consistent, giving you a range of shot patterns from "decent at medium range" to "are you kidding me, I thought I fixed this thing, that salty boye lied to me".

Here's an image of what kind of patterns I'm getting during gameplay:



Note that you can modify the other guns by using the same procedure.

The BFG edition gives you a shoulder-mounted flashlight. That's convenient, but DOOM 3 isn't about convenience. Even so, I hate the dinky radius on the vanilla flashlight, so here's how to mod it:

Go to pak005 --> def --> weapon_flashlight.def. Right-click to edit and scroll down to find "flashUp" and "flashRight"; these control the height and width of the flashlight's cone of illumination. I want to say the default values are "0 640 0" and "-640 0 0". I bumped these up so I don't have to run semi-diagonally to light up my path forward.



This is what it looks like. It doesn't light everything up, but it doesn't hurt my eyes as much, which is what matters.



Please leave a comment if anything is unclear or if you have any constructive criticism.