I have noticed just a small amount of rust on my APEX 50 cal barrel when I was using BH209 in that gun, I hunted with a fully fouled barrel in SW lower Michigan in heat, rain, & snow in Nov & Dec. I was able to clean it off. I have since been told that running a patch down the fouled barrel moistened (NOT SOAKED)with 90% Isopropyl alcohol will neutralize the corrosive elements while allowing you to be sighted with a fouled barrel.