Black powder itself is not corrosive. But if moisture or water hits it - yes, as it forms things like nitric, sulphuric and carbonic acid. And moisture is present in the air. I have shot many pounds of BP in my Shiloh Sharps (http://www.shilohrifle.com/
) over the years in silhouette competition and I have never had a problem with corrosion. And, I have never heard of a problem from any of the hundreds of shooters that I have been around that have ever mentioned corrosion as an issue. It is much easier to clean a black-powder rifle shooting my hand-cast lead bullets (distilled water is the solvent) than it is to clean any smokeless powder firearm. Don't worry about being stored around BP. There is absolutely nothing to worry about. Enjoy your Glock 27!