From the Holt's Auction description:

April 2025 Sealed Bid : Sale S0425 Lot 6750
F.P. BAKER 12-BORE (2IN.) BOXLOCK NON-EJECTOR, serial no. 87991,
https://www.holtsauctioneers.com/as...425+++6750+&refno=222043&image=0

F.P. BAKER 12-BORE (2IN.) BOXLOCK NON-EJECTOR, serial no. 87991, dated 1937, 27in. nitro barrels (wall thicknesses at 6 (six) and 17, some pits), tubes engraved 'F.P. BAKER. 1. GOLDEN SQUARE. LONDON W.1.' narrow rib inlaid 'FOR 2 INCH CASE ONLY', 2in. chambers, bored approx. full choke in both, automatic safety, border and acanthus scroll engraving, 13 3/4in stock including 3/4in. rubber recoil pad

Holt's can not sell any gun out of proof unless the barrels are cut for sleeving. This gun is listed for sale as still being in proof at .006" and I do not doubt it is. They make very clear that the barrels are .006" to their credit. A soda can is .006" thick. Just think how lively that gun will be to shoot. Talk about taking your hand into harms way. You should be able to flex or dent your barrel in your hand. I do not care where .006" is it is way too thin for me. Proof does not mean safe. It means within limits of .008-.010 of metal thickness from the last passed proof event. And where could you put pits in a set of barrels .006 & .017" thick? I wont be bidding on this lot. Read and understand all descriptions before you bid is sound advise.