The gun at Holt’s is “lined” and must therefore have Teague liners fitted, a process where the original barrels are lined full length with this steel tubes and re-proofed.
The merit of the process was that the beauty of the original Damascus barrels was preserved.
The disadvantage is that whilst with original or sleeved barrels a dent or bulge can fairly easily repaired, I understand that with lined barrels it is almost impossible.
The process has now fallen into disuse, and Mr. Teague is concentrating on his world renowned chokes.