When creating custom slot for magazines to go onto if the magazine is attached to the gun it works like normal but if you drag it out onto the custom slot the gun bugs out and doesn't allow for any magazine in the inventory base or custom slots to be attached once the gun is re chambered or the bullet is shoot out everything seems to work again perfectly fine

https://www.youtube.com/watch?v=hEKVu-GNDcw for an example of the process