Stimpy, there are cases where the breech face may need to be trued by just doing that, filing it flat. The only one that I've had that issue with is the .308 BB I just bought, not only was the breech face uneven, there was too much heaspace with factory ammo due to the uneven face, there was a gap in the middle of the barrel face when looking across from side to side, but it was touching at the top and bottom!. If the headspace is correct, there's not much choice without rechambering, but this barrel was a perfect example for cleaning up the factory mess. Fred has info on this on his web site too. I think it was oldbifer that had the same problem with one of his barrels. This would only be done before fitting the barrel and making changes to the pivot or latch shelf, and has been added to my barrel fitting help in the FAQs.
Tim