Re: Cleaning brass on old slings
I have used lemon juice for cleaning Brass in the past - you need to soak it for a while, maybe try a test first but should not hurt the leather. You could even rub some oil or grease (vasaline) into the sling first to protect it.
I have attched a photo of an old Capper/Decapper that I got and cleaned with lemon juice - as you can see it did a good job and did not hurt the wooden handle - it was very green and corroded when I got it
Enfield in NZ