Try a homemade electronic bore cleaner. You would be surprised at the amount of crud they get out of a barrel even after you supposedly gave it a good cleaning. I made one with a flash light, and it’s very good and inexpensive.

Here are some links of some different designs:

https://www.youtube.com/watch?v=-DMCEutvhDQ

https://www.firearmstalk.com/threads/making-an-electric-bore-cleaning-kit.31091/

http://www.predatormastersforums.com/forums/ubbthreads.php?ubb=showflat&Number=2615634

Just Google: “homemade electronic bore cleaner”