1) Equip primary weapon on your back (for example an M4a1).
2) Take the second primary weapon in your hands (for example a Mosin).
3) Disconnect from the server (the game crashes everytime at this stage for me).
4) Log back in to the same server.
5) Cloned weapon (Mosin in this case) will be on the ground and you will still have the M4a1 on your back as well as the original Mosin (which will be visible in your inventory below the backpack).