If you use a ramrod with out a bore protector bushing you may have worn the end of the barrel out of round. We used to see a lot of this back when we all shot PRB. I suspect some people have the same problem with Sabot guns. Also inspect the button a scratch on the button will also cause that problem. Certain kinds of oils [bore butter for one] have wax in them and it can cause a problem if it builds up but since it is clear it is very had to see. If you suspect this is your problem scrub your bore with boiling water and a stiff bronze bore brush and Dawn detergent. Lee