I've used CLR in an ultrasonic cleaner to remove a bunch of carbon out of a Titanium suppressor. The finish was marred, but the can was CLEAN when I got done.
I'll be honest, I haven't even owned a bore brush in over a decade, and haven't ever felt the need for one. I've been through about a half dozen custom barrels in that time and never dealt with any "carbon ring" symptoms, let alone a sever case of CARBID19. Sounds like I'll need to pick one up and get to work.
Film at 11:00.