Very well, understood & thank You! .. What are the chances of compromised integrity for the rest of the integral parts to the rifle, particularly when considering a 500 N.E.?When rifle barrels are fitted to shotgun barrels: cut the old barrels ahead of the chamber and fasten new barrels to them. Also used if bores are shot out and new barrels are fitted as the chambers may be ok. Very few gunsmiths can do this and completely hide the line where the two pieces fit together. Lesser smiths and/or those wanting a quick job engrave over the line as seen in the 4th photo.
The procedure is common on those building a double rifle from a shotgun. This way the extractors and lumps are used. Most shotguns are wide enough at the breech to accept double rifle calibers and this is done often to make a low priced double.