After a range session last Thursday I cked my barrel with a white patch and it came out brown again. This happens alot after a few days post range, thinking it is rust even after all the drying and lubes I decided to use phosphoric acid to see if it would react as it will with known rust. I wetted the brown streaked patch with it and no reaction at all. It will turn rust black on steel as a conversion coat but nothing so not rust. I believe the lube is color changing and gives a resemblance of rust color. Happy about that!
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