Help me find this thing.
 

I can't remember what it's called, I know it exists and it was the most awesome accessory I had seen in when I read about it last year.

It's a modification to a shotgun magazine that allows multiple tubes to be swapped via rotation to allow multiple ammunition choices. I have no idea how to even google for it.

Somebody here must know what I'm talking about.

It's called an RCI XRAIL (Roth Auto Index Loader).

Here's a link with more info on it:

http://www.thefirearmblog.com/blog/2...-index-loader/

So close! Same basic concept, but what I'm looking for was for a pump gun. Good find though.

They say they're not as easy to build for pump guns because the slide action takes up more room for the tubes, so it makes it very front heavy when mounted. I think the same company may make them, but I think the pump ones aren't fully functional to the extreme yet.

No this isn't it, what I'm looking for actually replaces the magazine and the pump. And it's not just extra capacity, you can swap around the magazines to choose between different ammunition types.