U are having a misunderstanding - Tennifer is not black - it is a grayish coating, that actually permeates the metal itself. The black color is an outer carbonized coloring. The black can wear, but the tennifer below will always be there - it supposedly is as hard as diamond.
That being said, Melonite is supposedly about the same finish as tennifer - just under an Americanized name. So, it stands to reason that it is the same principle. What U see wearing is just the outer carbon finish.
ALL semi-autos wear in that area - some more than others. The barrel drops down into the slide, and then scrapes the bottom edge of the metal slide as the action works. My SW99, P99, HK and Glock all have it, as have every other gun I have ever owned. Some show it more pronounced than others. Even when I get slides refinished on my polymer frames guns (I have hard chromed the slide on my P99, P99c and SW99), I don't bother refinishing the barrel. That wear will ALWAYS appear.
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