I just found this... A duplication glitch for melee weapons. Credit to Viva la Cakes at www.x360a.com I confirm it works as I made 8 Zeds Demise Katanas using this method. DOES NOT WORK for Molitovs, grenades, De Boms, or guns. ONLY WORKS with MELEE weapons. If this helped you please click "thanks"!
First of all i did not find out about these glitches. i came across some people in co-op who were doing this. I repeat i am not the founder of these glitches.
*** I recommend that you dont do this on your main character if you want the feel for the games survivability. Or if you have beaten the game then do what you would like***
Unlimited Weapons: Get the weapon you wanna duplicate hold LT + (Hold Y then quickly hit RT at same time) while looking at the ground, you will then duplicate your weapon.