Most of the shavings I've enountered were gone after the initial few boxes of ammo.
All the info on the slide rails metal, plastic have been stated..... but you might want to check your slide for sharp edges where it rides on things. Not too uncommon to have a little sharp edge or burr, which one hurt anything, but you can smooth them down with an emory board. All three of my Kahrs had a little burr where the half moon cutout for the disconnector/triggerbar was supposed to ride up and down. A few seconds cleaning that up a little will make things less likely to shave plastic when you disassemble for cleaning.
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