Never leave Sweets in the bore over night!!! Also use a nylon brush and a coated jag.
My understanding is that with any ammonia based copper solvent that the damage is done if you let it dry in the bore. This is when etching occurs as the ammonia mixes with oxygen and becomes corrosive (ammonium oxide? not sure). If you plug your barrel and fill it with Sweets or whatever this does not occur. But I have never had to do this and don't want to test it on a good barrel. An old Military or factory barrel that I was about to give up on anyway I would do this as a last resort.
