It is far more costly to fabricate a damascus barrel blank with sufficient breech thickness to allow machining out a chopper than to fabricate one suitable to dovetailed lump construction. On the other hand, it is only slightly more costly to cast/forge a fluid steel blank with the chopper on it. Note, the chopper must be integral with the rest of the barrel and not just welded on. There was a period of some 50 years, say 1880 to 1930, when various shops and craftsmen within said shops were skilled in both methods. They, no doubt, used which method was ordered, more profitable, easier, or most comfortable.
I'm the only person I know of who has actually had a dovetail lump failure (OE cold joint). I was quite amazed at what a small spot of braze had lasted since 1921. Repaired, reproofed, back in service, no issue.
