Jack,
I have seen guns with both types of ribs from the US and Europe. In a few cases, e.g. Lefever, we know he was buying tubes from Europe, but also had his own matting machine. I can only assume he was buying the rib stock locally, perhaps directly from a mill.
I believe that ribs were a product of the rolling mills in Belgium and were mainly fluid steel. Birmingham may have been a different story.
I would really like to find sales brochures from rolling mills from a variety of countries.
Having said all the above, I have nothing to back it up, so I could well be wrong.
Pete
