First off thanks for taking the time to look at this. I'm not completely new to the ar platform I'm in the military and run a colt m4, but doing all this research is starting to get me confused... Just a few things like 1/7, 1/8, 1/9 twist , chrome lined barrel, pencil thick barrel .....ect ect... Basically I need a quick rundown on a ar15.. I want a good one that can take a beating at shooting schools and be tough enough to last a Long time as my go too gun when **** hits the fan... But I don't want to drop a hole lot of money on one at the moment. What are the good brands to stick with and what are the iffy ones to stay away from...I would like to have a low gas block cause I plan on putting a troy, Daniel defense, or noveske free float rail on it. Here's what I want to build/ make it look like..