They had a patent on it, since 1938, so it most likely was well into the millions.
The only Mossberg I have right now is a TR42 smoothbore .22. They made a miniature clay bird thrower called the “Targo Trap” that bolted under the barrel and chucked these 2 9/16” birds. The barrel was threaded at the end so you could screw on a rifled section and shoot it like a regular .22.
Lucked across the gun, finding the trap gadget and a hand full of targets took a lot longer.