I have my fathers older Ruger 6mm Rem that is giving me fits. The barrel had been neglected for years without being properly cleaned until recently. Accuracy was poor and I was not able to get the proper sized patch down the barrel without using a mallet...got stuck halfway down! Went thru some rigorous cleanings with different solvents without much success. Was advised to use JB Bore paste and it made a world of difference and regained accuracy. My problem is it fouls up so bad after a few shots you can't get the regular patch in the barrel. I did the JB cleaning again and the patch goes thru without a problem. I just got one of the teslong Bore scopes and checked out the barrel after cleaning and saw there was still a lot of carbon fouling in the first few inches of the barrel. Hit it one more time with JB and it looks much better. My question is this- is it possible that there was so much carbon build up that even after many cleanings and 2 JB treatments a barrel would get so fouled in 10-12 shots the patch can't get down it? The patch literally gets jammed at the end of my Bore guide. Would something else be causing it? I took a picture of a black ring that is at the end of chamber in front of the rifling. Is this a carbon ring? Sorry for such a long post but this is new to me. I'm a hunter and shoot for fun and just getting into the more precision reloading and barrel cleaning. Many thanks.