Please, someone tell me how to make that! That is awesome looking! Ghetto-fabulous or not!
These two pictures were posted by a gentleman named IuardoEdl Gonzaga on Facebook (it's a weird enough name that if you search, there's only one), in a California-based airsoft classified group I belong to. He is or was selling the one on the right for $20 plus shipping, but I bet he'd make more if there was demand. Here's what he posted about it, but I'm not sure if he's keeping intentionally vague to protect trade secrets:
"I did modify the shell to accept the mag. I use dremeling, files, and spacers to prep the shells for the high cap mags."
"Yes, the shell allows the high cap mag to lock into the original magwell without modifying the shotgun. Only modification is done to the shell. And to remove the stopper from the top I the high cap mag."
"I use several layers of epoxy. Liquid nails actually works better to adhere the mag to the shell. I haven't had any problems so far."
"The high cap door is still accessible from the top."
I can sort of visualize how he did it just from that and the pictures, I think if I had all the parts in front of me I could make it work. You just gut the spring and follower out of the shell to make it essentially a giant feed tube, and remove the catch on the high-cap's feed port, relying instead on the catch at the end of the shotshell.
