Waaay more than I understand, but manganese sulfide inclusions apparently can form in 4140, today's standard barrel steel
https://etd.ohiolink.edu/ap/10?0::NO:10:P10_ACCESSION_NUM:case1057696631

I can't provide documentation, but believe most Italian, Remington and Japanese Browning, barrel tubes are proved, using a hydraulic device, by a representative of a batch, not individually. Finished guns are individually proved per CIP requirements.

Interesting image of checking the monobloc joint visually and with US
http://www.fieldandstream.com/photos/gal...y-tour/?image=3

Finished gun "after being proofed and tested for POI"
http://www.fieldandstream.com/photos/gal...-tour/?image=10

https://sites.google.com/a/damascusknowledge.com/www/home