So the question is who modified the Pieper technique specifically for replacing barrels using the original breech section?

I couldn't find an online copy of the 1954 Rules of Proof but possibly someone could see if the sleeving rules are contained therein?

And a sleeve job that was apparently inexpertly performed; 1891 10g GHE sleeved to 12g and restored...for awhile wink

[Linked Image from photos.smugmug.com]