Asklemmy

I hope folks read more than just the title. So im watching a show with a gun exchange and the person has to reload and you can see they are nervous to get the new magazine in so they can fire again and it made me think. Do any guns have two magazine where you can either manually switch to the other magazine or maybe automatically do it when the first one is empty. With the idea that if you need to fire while in the middle of changing out the empty magazine you could. I feel like this seem obvious enough that someone must have tried it. I mean considering the crazy gun things I have seen. Since im not aware of anything I figure if it has been done it had an issue or was just not useful enough to make worth it. So for the folks that are really into guns, especially wierd protoype ones. Has there every been anything like this?