After the Dying Light patch 1.05 it is possible to duplicate any weapon as many times as you wish. The game is mostly melee-based with the majority of fights using melee weapons.
There are more than 100 weapons that can be used and more when players begin crafting new weapons.
How to Duplicate Dying Light Weapons:
Your very first step will be to acquire the weapon you want to duplicate and then go to the Infamy Bridge. You will get the exact location of this bridge from the video at the end of this post. When you see the bridge, go under it till you see an abandoned wooden simple boat (or whatever you want to call it!)
To duplicate your weapon you will need a grappling hook too, now all you have to do is, look down at the boat and grapple it. It will duplicate your grappling hook along with the weapon that you are equipped with. You can collect all the weapons from the surface of the boat without any problem.
You can duplicate as many weapons by repeatedly doing this glitch as you want, irrespective of a player being at any level. Currently you can only duplicate your weapons from under the Infamy Bridge, but this location should not be a big issue since this glitch is damn easy to perform.
Check out the video on how to duplicate Dying Light Weapons: