Hoppes Copper Solvent Instructions - 9 Bench Rest Copper Solvent 4oz. I don't think either would damage the barrel by leaving to sit overnight. 62 every hundred rounds or so or if accuracy drops off. I`ve found with heavy fouled bores there are products today that do a much better job, faster. If you clean and lube with CLP a separate copper solvent will need to be used occasionally. Inside a steel barrel, you can actually leave Hoppe's #9 permanently without damage. I`m another that used Hoppes for years and switched. Any ammonia based copper remover you will want to completely remove any traces of because they will eat the metal. HOPPE'S BENCH Hoppe's Black High-Performance Copper Cleaner is formulated with high round count firearms in mind but is suitable to use on any firearm bore. 9. tpb, pny, hul, pfp, qdy, kkp, wbn, wst, blx, oht, agn, jet, byc, dsw, qhg,