Just played it and ... after one year i've got ot say this game is becoming a serious and well done fps...
Need a few touches..-like speeding the double barrel reloading time...and adding a double jump...
Just a thought

Install 7zip.

Go to the kp1 folder in your game directory i.e. "WRATH Aeon of Ruin\kp1\

Open "WRATH Aeon of Ruin\kp1\pak001.pk3\"

Edit "pak001.pk3\data\weapons\shotgun.txt"

set // time fire 1 to 1.2 or even below.

That's it. Happy hunting.