General Credits (applies to all guns):
ID Software
Craneo
AliensTC/Brutal Doom (muzzleflashes)

Pistol Credits:
JoeyTD
Minigunner

Shotgun Credits:
DoomNukem
3D Realms

Double Shotgun Credits:
DoomNukem
Pa1nki113r
Exhumed / Powerslave
Raven Software
Doomedarchviledemon

Sniper Rifle Credits:
DoomNukem
Carbine Dioxide
Zrrion the Insect
TODM
Gearbox

Jack's Gun Credits:
DoomNukem
SolidSteak
Carbine Dioxide

Fire Grenade Credits:
Capt. J
Uboa
??? (brutal hands, animation)

Sound Credits:
Valve, Counter Strike (Machinegun, Pistol sounds)
CturiX, Madness Combat (Shotgun, Double Shotgun, Jack's Gun, Sniper Rifle sounds)