rgchristensen wrote yesterday at 11:35am:


It is carbon/carbon,lead, well known, well understood.

burntwater wrote yesterday at 8:49pm:


Rick,

I beg to differ.  Here's what a Google AI search has to say:
Yes, oxalic acid is effective at removing carbon-based stains, specifically baked-on carbon, food, oil, and mineral deposits, often found on stovetops, exhaust stains, and in industrial applications. It works as a mild abrasive and chemical cleaner, frequently found in products like Bar Keepers Friend (BKF). 
Key Details on Oxalic Acid and Carbon:
•      Stain Removal: It is highly effective for cleaning stubborn, burnt-on carbon deposits on surfaces such as glass stovetops.
•      Exhaust Stains: It is often used to remove carbon exhaust stains on marine vessels (GRP hulls), particularly when mixed with paste to improve adhesion.
•      Mechanism: It acts as a reducing agent that chelates (binds) metal oxides and breaks down mineral scales.
•      Alternative Uses: While effective on carbon deposits (soot/food), it is famously known for removing rust (iron oxide) and mineral deposits rather than elemental carbon.

And here's a couple of bore photos of my Stevens 44 22LR with a Shilen ratchet barrel & match chamber.  Using the BKF on a O-tip was a lot faster than with using Bore Tech C4 on a Q-tip.

Before & after photos.

Wayne