Metal’s worst enemy is rust. And because Navy ships, Air Force’s jets and Army’s tanks are made of metal, rust has become a long-time enemy of the Department of Defense. And believe it or not, it has been costing the government $23 billion every year to fight it.
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http://www.mycleaningproducts.com/rust_products.html Here is a video a satisfied customer sent of Rusterizer, it appears that Rusterizer can remove rust from clothing, metal, and just about anything else without wiping. Including rifle slings.