I'm would like to start an AR build once I complete my bolt action rifle but honestly I don't know very much about them. For starters would there be any reason to get a piston over a gas operated AR other than cleaning and maintenance? I'm told that AR-10's don't have as many interchanable parts but I'm not really concerned about that (unless I should be lol). I would prefer the .308 over the .223 for range of 600+ yrds unless I am mistaken about that also. I guess what I'm asking is simply for someone to point me in a general direction of where to start with this project. I want to know as much as I can before I just start throwing money around and making expensive mistakes.