Basic technique is to marinate the rusted area in a rust busting penetrating oil (Corrosion-x, Kroil, WD-40, etc) to soften it up enough to go at it with something made of a "soft" metal such as brass or copper. If it doesn't break apart easily or still feels solid, let it soak some more.

An old trick is to use the edge of a (real) copper penny to gently scrap away the rust, in the process since the copper penny is softer than gun steel, it will leave copper "scrape marks" that will come right off with an oiled cleaning patch.

I've successfully used a combination of a soft/medium bristle cooper & brass brushes, #0000 bronze wool (do not use steel wool, the ultra tiny "hairs" that come off work their way into places to start new rust problems), tooth picks and a lot of swearing.

Don't be in a rush, let the oil do it's work, not your elbow.

For rust protection, that will depend on how humid it is where you live, a light coating of oil (Kroil and BreakFree are often mentioned) as well as keeping them in breathable BoreStores is what I do... and being in a safe, a dehumidifier rod is a must in the winter months.

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Conrad
SWCA #1830 SWHF #222