Shoe Lump system has the lumps machined from solid with a large platform on top and the lumps protuding beneath.
The platform is precisely fitted and brazed to the underside of the barrels.
This platform is like a "shoe" attached to the barrels and actually forms the barrel "flats".
The shoe usually continues around the lower edge of the chamber portion of the barrels and is usually visible from the side with the action closed.
A good photo of shoe lump barrels can be seen in Safari Rifles book.
Look for the Jeffery 600 NE snap action underlever.
The edge of the shoe is clearly visible.