I made my statement from memory and now that I have 'The Modern Shotgun' by Burrard in hand, I see I may have slightly misquoted Major Burrard. Here is verbatim what he has to say which can be found on page 31: "the best chopper-lump tubes, however, cost sixteen times as much as the cheapest grades of ordinary steel tubes, and so it is not difficult to understand why their use is restricted to high-grade guns. At the same time the advantages of chopper lumps are so great that I do not think it unfair to state that no gun made to-day can be regarded as a really 'best' grade weapon unless chopper lumped". Now, that was in the 1930's and before the advent of CNC machines and other technologically advanced tools. So, I'm not surprised with CNC machines in this time period that it is only twice as expensive to fabricate chopper lump barrels. But one must remember, original Model 21's were made prior to the advent of the modern CNC machine.
