Did you look down the bore using a light at the other end . Look down the bore with a bore light . Wal-mart has a nice winchester one for $5 . If the bore walls are still shiny smooth with no dull areas or pitting it was probably not rust .
After just writing the above I looked up KG 12 . It is a water based bore cleaner and you left it in your bore for a long period of time
What is a long period of time 20 min or 2 months ? 20 min should be no big deal but if you ran a wet patch down the bore and then put the gun up for a month . that may not be good .
First they came for the communists, and I did not speak out - because I was not a communist , Then they came for the socialists, and I did not speak out - because I was not a socialist , Then they came for the trade unionists, and I did not speak out - because I was not a trade unionist , Then they came for the Jews, and I did not speak out - because I was not a Jew , Then they came for me - and there was no one left to speak out for me.