Hi Brad,
Welcome to the forum! You may find this photo helpful, it's of an original salt blued 1939 Mauser P08. It appears to me that the barrel was polished on the lathe, whereas the flat surfaces were "sanded" on a perfectly flat surface covered with a very fine abrasive. If you try to duplicate this finish it's vitally important to maintain the flat surfaces and sharp edges. Good luck!
Norm
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