I've been wondering this myself. I currently have a Sendero CF barrel in a Sendero barrel channel stock. I was thinking about a 3b on its next barrel. @WapitiBob, thanks for sharing. It looks great.
It's a 6mm cm. I can get 5/8x24 on the bartlein #3, XCaliber #5, Brux #4, etc those all end at .670…but I'm being told it's not recommended to run direct thread on those.