I got my first ar 15. It is a used S&W M&P 15. A couple of weeks went by before I had the time to try it out. It seems to have a broken fireing pin. No marks on the primers at all. As my SHTF gun this makes me doubt the durability of the gun. Are these type of break downs common to the ar? If so I may need to go with a Mini 14. I've owened two of the Rugers and never had a problem. I wanted more accuracy than the Rugers but can not accept break downs in what may be a life or death situation. I'm want to stick with the 223 as I have about 800 rounds and one Mini in the gun safe now.