Boric acid is also effective and inexpensive. You can buy it as roach powder at the store. Mix six heaping tablespoons per gallon of hot water. Make sure any oil is removed before the soak. I soak for at least 30 mins. Then, rinse under hot water while scrubbing with a new green ScotchBrite pad. It's very effective. If the rust is heavy, I'd wire wheel it first. It's what I use for rust and bluing removal.
Regards
Ken
I prefer wood to plastic, leather to nylon, waxed cotton to Gore-Tex, and split bamboo to graphite.
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