Fred, I agree 100% with you. Even enlarging and studying your pics hard, it is difficult to see the filing you speak of. First off, we all know that barrels actually increase in diameter as they get to the plug, and so we look at a rifle knowing this is the case, and because it is the norm, we can't see anything else. Secondly, the lug in the breech plug cannot be bent down directly behind the barrel, so we know that the tang will start to bend about 1/2" behind the lug. This is where your filing technique shines. And as you say, care is required not to file the tang so thin that is is easily damaged.