The device you are referring to is a Cartridge Ganoche. They are available in 50, 100 and even 200 cartridge models. It was designed for the loader- I doubt the shooter could support a 200 cartridge and still pick up the gun.

Fine Shooting Accessories still lists them but he has discontinues the loadmaster. They also pop up on Ebay.

The loadmaster is the device of choice on driven hunts. It presents two cartridges in the proper orientation. As Dr. P notes- it helps on tower and driven birds.

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