1. I have a M&P15 adn want another AR adn was thinking of building a RRA with a 10.5 barrel, but also i am considering getting an other M&P and switching the barrel for a 10.5 and my current one for a 16 from RRA, is there a better way to do this? 2. What does everyone think about the RRA barrels and will they fit a M&P? Wanna kill these ads? We can help!