I saw a number of postings to various on-line gun forums where people reported doing this. The one that I most remember was from a guy who discovered that vinegar removed bluing when the Taco Bell hot sauce dripped onto his gun because, no joke, he was going to the range and carrying his gun and some tacos in the same paper bag. When he got to the range and discovered the mess, he wiped off the hot sauce and saw that the bluing came with it.
His unorthodox and rather inappropriate carrying method certainly got my attention. I will keep my tacos and my pistol in separate bags, but at least we can learn from his observational chemistry. Taco Bell sauce lists vinegar as a primary ingredient.