Those rings look like rough chamber reamer marks. Your neck turner should not touch the shoulders (except perhaps for about .0002" into the neck-shoulder junction.
I have the Forester trimmer/turning attachment, and do not like it. The cut is too coarse. If I am removing say .0008" or more from the neck, I will rough cut about half with the Forster and finish with the K&M.
I have the Forester trimmer/turning attachment, and do not like it. The cut is too coarse. If I am removing say .0008" or more from the neck, I will rough cut about half with the Forster and finish with the K&M.