Some shotguns permit you to "float" a shell on top of the carrier, while one is in the chamber, and your magazine is full. In this way you can get the maximum capacity out of your shotgun. In this video the shotgun I'm demonstrating to "ghost load" is a M4 Benelli, with the full length magazine tube I put on it, I have a nine round capacity with carrier loading.
Carrier loading is included in the USMC's operation manual for the M1014 (the Marine version of the M4).
If you guys know of other shotguns you can do this with, let me know.
Here's the video: