I mean this in all sincerity and with respect for Kirk Merrington, but if he doesn't have x-ray vision he can not, and likely will not, provide any assurance/guarantee this barrel is safe.
One important issue that has not been clarified.
What, exactly, is the chamber length?
Below are radiographs of 2 "inexpertly lengthened" 16g chambers
The right arrow
The left arrow. Just FYI the right arrow indicates where the thicker breech segment was butt welded with the mid-barrel segment
The 'J' is the Belgian "rough forged tube" maker; likely Janssen Bros. You can see one little bulge top left
Threaded Mode