Ok, I'm fairly new here and the only gun I have owned so far is the 1911 that I currently have. I've been looking at building an AR-15 for a SHTF situation and was wondering about the .308 chamber for it. I have a few questions about it and would like to use your experience here. First of all, will a standard AR-15 lower work with a .308 upper? Second, will a standard AR-15 mag work with .308 win rounds? Third, what is a gas piston assembly for an AR-15 and what does it do? Last, what is the difference between an AR-15 and an AR-10? Thanks for your time and help.