Attach a Hoppe's 12 gauge tornado brush to a shotgun cleaning rod and chuck that up into a drill, have no further suggestion on what solvent to use. It's how I remove lead fouling.
https://www.ebay.com/itm/225020120626?_skw=12+ga+tornado+brush&itmmeta=01JC9NWAJCR1ZQSJ00RM357VB4&hash=item34643e8e32:g:t-8AAOSwbqFinmDx&itmprp=enc%3AAQAJAAAA8HoV3kP08IDx%2BKZ9MfhVJKn3YSuChYYBLMhYSlVwae2CDMoAy%2BhY%2BeTy2WLum7oPECVsVy7zFvFIZU1ZwkaK0gP6aAPmXyDYzhbVR59iGulasI5qamDuLhsuYTS5rqIMGj9gzqZ2NqWwV2AWPYJlKiQRVd9hBz1NKCD4i3EqSNc%2BzkAeYC1vYgGovy29IFeHg9dYPYk%2FuN3fYu4uQwHN6UmDpkZzHLZ45Hz896WPWR0rF0yABr%2BvrYF5M3cZ%2BDvRJvfHDMJCrZa72329nhwNpOhFx4ZJNdWDhduojrgTsAClRZeo9Z8kAx8xzA7AUJSiTw%3D%3D|tkp%3ABk9SR6qp8bXiZA