After my post above I read what Toby had to say about his colleague that is an experienced tig welder of barrels and his post weld temperature to such a high temperature makes sense to me.
I learned how to make the cutting tools to join barrels for sleeving to the breech end of the original barrels without the seam showing, hence I do not have someone to weld them and have not encountered the welding problems. A successful jointing is made of barrels where one edge is 90 degrees and the other edge is about 1.5 degrees concave, or less than 90 degrees--proper making and sharpening of the concave cutting tool is critical. Gunmakers who do not have in their shop milling machines, lathes and diamond plate cutting discs (to make/sharpen machine tools) have a difficult time sleeving guns with an invisible joint and have to resort to tig welding.
