I Have two lower receivers that I bought from a friend in California and I'd like to sell them. What he told me was that they are both pre ban. What I need to know is if that makes them more or less valuable and how could I verify their age? One is a colt sporter match hbar (serial # mh054824), the other is a bushmaster xm15-e2s (serial # L175475. Any help would be much appreciated.