Odd rifle caliber


New Member
I found this old smooth bore rifle in my dad's collection He didn't know much about it. It's too small for a .410. A 9mm catridge slips into the breech and gets stuck. The muzzle is smaller than 9mm.
I'll put some pics in my album.

Any ideas?

Found some markings

I found some markings under the forearm (I can't seem to upload pics)
There are three German proof marks, a crown over an S (Indicates Shotgun), a crown over a B and a crown over a U, both seen to indicate single proof, foreign arms.
There is a 78/41 marking inside a circle. I can't find a reference for that.

There is also a stamp that says 8,3mm. I figured that meant 8.3mm caliber, but the reference I found seems to indicate that might be the cartridge length. Which would make sense since it's a shotgun?

There is one more marking:

Not sure what that indicates.

So, this is a single shot, break open German shotgun of some sort...
One way to upload pictures here is to create an account on photobucket. Take the pictures and download them from your camera or cellphone to your computer. From the computer, upload these pictures on photobucket. If you are looking at the pictures on the photobucket, you will see a list of different options on the right side of the screen. I think there are four or five different options, depending on what you want to do with the picture or the gif image. The option best for forums is called (IMG) I think. It will copy the picture and you can paste it in here and you can get the help you want.
I can see the pictures, unfortunately, I can't help you with your queries. George and Remington are good with these things. They will help you, I hope.