The .GunProfessional part is an “attribute” and is the name we will look for in the rest of the source code.
Use a tool to search the “content” of the text files in the Program folder (a source code tool like CodeBlocks will help, or a sophisticated, yet free online, text editor like Notepad++ will search the content of an entire directory and its subdirs). Searching for GunProfessional, we find the effect for this one is calculated in Program\loc_ai\LAi_fightparams:
p = p + 0.25; //This refers to the 25% increase
p = p + 0.1; //This refers to the 10% increase for Gunman/The Shootist