I undid the thing.
Slap the folder in mod_overrides. (don't slap it too hard tho)
If you downloaded the fast reload addon, slap it in mods. (it doesn't show me how long it takes because I have a rebalance mod but it works)

Note : if you already downloaded the first version of the mod, remove the part you put in the mods folder. (it's not needed anymore)

Known issues :

• New magazine won't have any bullets when reloading from empty, the IZHMA and the LEO do that too so I dunno if it's the mod or the game's fault.