1. Have any rifle with a magazine in hands and a magazine for a different rifle in your inventory.
2. Open inventory.
3. Drag magazine from rifle in hands onto a magazine that it cannot swap with so the box is highlighted red.
4. Magazine will move to the inventory and gun will become bugged.

I produced this on a modded server, however I used vanilla weapons. Tested with M4a1 and AKM
Here is a video of me reproducing it, apploigies for the Smiths in the background lol