ORIGINAL: Triple Se7en
If you make a mistake cleaning/storing with Bore Butter by applying it over trapped moisture in your rifling, rust will form overnite. Also... the use of Bore Butter with sabot/bullets is highly discouraged. It very easilyturns goodshot groups into bad ones ... especially in colder weather when it thickens fast from outdoor exposure.
I had this very thing happen in my inline rifle. I was storing the rifle for the end of the season and wasn't planning on touching it for a while. Fortunately I caught it before it got too bad and the rifle still shoots well.
It was a bear to clean out all that brown gunk and you can still see some of the damage in the barrel, but it still shoots well. I threw out and swore off bore butter.