If the brushes are cleaned off they will slowly eat away if you leave any solvent on them and also redeposit garbage like others have said. Gunsmith friend has no problem with bronze match brushes but advises against using JB compound. Based on how his guns shoot I respect his opinion immensely. I really don't even like ammonia cleaners anymore and just use shooters choice, butches , montana extreme whatever is available with a quality brush and patches . Once a year the guns get a Foul Out III run on the barrels and never have problems with any of them.