I'm looking at getting one and the description says "The inside of the frame is marked M971 and M713." What does that mean? Also, the website says it's double action, does this mean it can also be fired in single action? Is there a way to tell if it was made before or after Taurus acquired Rossi? It has a non-fluted cylinder if that's any indication. Lastly, what's the difference between a 971 and 972? Thanks.