As i said, the magazine capacity works just fine. But the durability does not. We tested this on main server and a test server with nothing that could modify it and still does not work.  below is a sample:

"firearmmodifier.2": {
          "SkinId": 0,
          "MagazineSize": 60,
          "PreloadSize": 4,
          "Condition": 300.0,
          "InfiniteCondition": false,
          "InfiniteAmmo": false,
          "DropOnDeath": false,
          "WeaponName": "",
          "AmmoType": ""
        },​

That is only set for crafted weapons. Currently + player must have the permission

so only crafted will work?  is there a way to make it work with all weapons craft or "found"

perilous

so only crafted will work?  is there a way to make it work with all weapons craft or "found"

That is correct only crafted as it says on the docs.

Not with this plugin no. 

That would have to be done on some kind of custom loot spawner plugin and they would have to add support for it. 

I have been working on condition and custom item name features support for the guishop plugin for about a week or so now and just for me to support it for GUIShop and StackModifier I had to control everything myself basically. And It's still not quite 100% but really close.