Fig 5 is usually referred to as the "Shoe Lump". My J P Sauer & Son/V L & D Knockabout sidelock has this type of lump. There is no mechanical advantage to this shoe lump, but it does have a very large brazing area.
There is also what is normally referred to as "Conventional" which is similiar to the dovetail but without the side points, the lug just tapered to a point at top & fit between the bbls. As best as I can see the braze lines my Lefevers all have this conventional contruction. They of course bolt into the rib extension so there is little downward pull on the underlug.
As I recall Winchester moved their dovetail further foward than shown in Burrard's diagram. This at least partianally elimanated on of the major objections to its use, that of wider spaced breeches. The other objection is that of necessity the lu has to be built of bbl steel, a seperate lump can be built of some form of tool steel & will thus normally be harder.
