Is there any way of cleaning up old solid fuel lines and removing the oxide that has built up, without also removing the copper coating?  15992.jpg You have insufficient rights to see the content.  15992.jpg You have insufficient rights to see the content.

Try to find a product called micro,it is a chemical cleaning solution.
You water it down to the required strength and soak the items.
I, in the past used it for cleaning my cases when i did a lot of hand gun shooting.It got the cases super clean for reloading,so you can imagine if it will remove gunpowder residue,i think it will do what you want.
(try a gun shop.)