[wterrell]

If my understanding is correct, viewing a barrel and receiver oriented as per Dwight's pic, a retreating barrel would have the upper witness mark to the right of the receiver portion of the mark. I do not mean 1/64 of an inch, but rather 1/192 (.005) of an inch as an extreme to the eye. A greater mismatch than 1/128 would indicate removal and reassembly of the barrel to receiver by a skilled gunsmith.