lbdavis makes a good point...
My SB had four rings in it. I know that they are all different, but that could be your problem. If you are able to thread the Packing Nut on four or five turns, you may not have enough material in there. On mine the new material allowed to just get barely one full turn on the nut once the threads were engaged. If your doing more than say two full turns, you're probably material short.
If you liked my advice/response, give me some rep points. If you didn't......well what do you expect, it was free.