rafsob
All black powders and substitutes are hydorscopic and will draw moisture, which willcorrode metal.
You might better check more into BH... it is a black powder sub but it not the hydroscopic... it is really a progessive burning smokeless powder that you might use in a regular rifle. It was engineered to match the power and volume characteristics of Swiss/T7. If you request a government MSDS sheet it should be apparent or just open a jug of the odor will tell you right away. It is not NC but sure has a bunch of Ether in it.
But then again for this topic what does it matter?... any barrel bore that is unprotected from moisture or climate is suseptible to rust... even your centerfire barrels.