My build.....AR build anyways.

A $500 AR is kinda like cheap tires or cheap brakes. They're 'the same' insofar as they look similar and are the same shape.

I could go through all the things that those $500 guns do wrong, but it would take all day. Suffice to say, a 16" barrel with a carbine gas system is already a load of crap.

The bolt carrier groups is where the majority of the flaws are, however. Bad finishes, bad dimensions, bad chrome. Put it this way: it'll probably be flawless for 50-100 rounds. Anything after that is pure luck of the draw. Same goes for the barrels, bolts, and extensions. Most of the cheap guns are using less-than-good steel for the bolts, and aren't doing the mag particle and high pressure testing to ensure they're good. The barrels are typically made from cheaper 4140 vs the CrMoV steel that is better suited to resist throat erosion, and twist rates on the cheap ones tend to be 1/9 which is good if all you shoot is 55gr ball.

At the end of the day, that $500 would be better spent on a 10/22 or decent savage bolt-gun. Having a decent semi-auto is going to run over a grand to start. Starting with a $500 gun will cost over 2 grand ;)