There is a bug currently in the experimental .63 patch with how magazines and guns interact with one another. Say you have an empty U-70 in your inventory and you find a magazine for that U-70. If you press f to pick it up, it will automatically put it in the U-70 without ever going into the reload animation. Not only will it do that, it will practically make the gun useless. You aren't able to take the magazine out and you won't be able to shoot the gun either. This bug has happened to me and my friend on multiple guns including the U-70, Scorpion and MP5. We have since been avoiding the bug altogether by looting through the vicinity and dragging the magazines into our inventories.