Saw one of these devices about a month ago, just remembered it today. I vowed to remember the name of it, but promptly forgot it.
Anyway, it was on a Stevens singlebarrel shotgun, off the the left side. In principal, it worked like the magazine on a pump shotgun in that it stored a few rounds in a spring-compressed tube, and when you broke open the gun, you could pivot this magazine over the breech and load the gun. It was weird, and I doubt it was helpful in speed reloading, but there it is.
I wish I could remember the name and furnish a picture of this device. IIRC, some tool company made it.
