Dear Researcher;
First let me say that I have appreciated all the information about guns that you have contributed to this forum as well as publications through the years. Your knowledge is truly remarkable. And I expect that you have a very detailed opinion of the answer to the question you presented.
Decades and decades ago I had a blacksmith shop and forged many items with tools being my favorite items to forge and finish.
Chopper lump barrels are forged from large "lumps" because the finished barrel must have a lump on the end that can be finished into a flat inside surface to where the other barrel's flat inside surface can meet it. Those flat inside surfaces can be milled at an angle in order to have the correct conversion of the barrels at the muzzle. However dove tail barrels as well as shoe lump barrels can start their life in the forging shop in much smaller "lump" size before it it forged (or sent through a rolling mill) into a round bar for boring into a shotgun barrel or rifle barrel--it takes 200% or more forging work (power hammer usually) to forge a chopper lump barrel and hence a great deal more expense.
View this video and see all the work that is required to forge a chopper lump barrel:
https://www.youtube.com/watch?v=2Buoivte49cOn another note: Modern shotgun or double rifle barrel set on finished guns/rifles usually come in 3 forms: chopper lump, dovetail and shoe lump. Several years ago I began to think about why shoe lump barrel double rifles are only made by the Germans and French skilled gunmakers. I decided I would build a double rife with shoe lump barrels. As I had never seen a shoe lump barrel set made, much less the machining of the shoe lump itself, I spent 6 months thinking and calculating how the shoe lump should be made (with a milling machine) and how the barrels would be brazed to the shoe lump all in order to made it suitable for regulating the rifle to shoot to a point of aim 100 yards away. I spent another year in building and regulating the double rifle. Long story short, I now understand why it is so difficult to build shoe lump barrels--Jack Rowe the English gunsmith used to say that shoe lump barrels were stronger than chopper lump barrels. Shoe lump barrels are very strong, but in my opinion after building some, they are not stronger than chopper lump barrels.
Kindest Regards;
Stephen