This Backun barrel cracked on two sides, right through the wood retaining ring. It would have undoubtedly spread eventually and the leaks would have created serious playability issues. Pinning the retaining ring was impossible due to the small work area, so I wrapped a carbon fiber band inside it instead.
These barrels are put together in three pieces, the two large rings are adhered to the barrel after it has been machined. They are designed to prevent the thin walled barrel sockets from cracking. They failed. I suppose traditional metal rings would have been better after all.
The two holes drilled into the body of the barrel provide a termination point in which the crack will stop.
I received very helpful advice on handling this repair from several techs I respect highly, thank you to all of you.