My build.....AR build anyways.
Not trying to argue, but for the sake of discussion..
Haven't heard about EOtech? Won't hold a zero in changing temperature conditions.
That is during very extreme temps. I have ran several EOTechs in some pretty extreme temps and conditions, and the only issues I ever had was shut-off once while full-auto with a MK46. That was easily fixed with the addition of the little foam donuts to restrict battery movement. That being said, for pig hunting in heavy brush with my 300BlkOut, I run one of the cheap Primary Arms MicroDot clones. It has been 100% reliable, and its def not babied. On my Mini-G, I run a Burris FF3. Both cheap but good options for a red-dot if you want to go that route.
I could go through all the things that those $500 guns do wrong, but it would take all day.
The current M4 carbine the military runs costs $550 for the gubment, and in civilian trim hovers around $600 for the private citizen, so I would consider it one of those "$500 guns". What this rifle does right is; make ownership affordable to the average person, care and feeding is simple and cheap, and shooting it is even easier. It's not going to outperform a MK16 Jager Karabiner from SWORD International, but it will probably outperform it's new owner in every way.
The bolt carrier groups is where the majority of the flaws are, however. Bad finishes, bad dimensions, bad chrome.
You often see this with the cheap "tacticool" boutique stuff with zombie slayer BS engraved into them etc. No different than buying an Autozone hood scoop and plastic chrome stick on flames. Stick with basic milspec parts from an established manufacturer and you won't have an issue even at the lowest price point.
Anything after that is pure luck of the draw..
research the manufacturer, buy from a vetted source, no luck involved. problem solved.
The barrels are typically made from cheaper 4140 vs the CrMoV steel that is better suited to resist throat erosion..
do you honestly feel this is a concern for the average AR owner? take the expected life of a 4140 barrel, multiply that by current ammo prices, now compare that to the budgetary restraints on the guy shopping for a $500 rifle in the first place.... you get the idea.
twist rates on the cheap ones tend to be 1/9 which is good if all you shoot is 55gr ball.
this is
completely false. 1:9 can run heavier rounds just fine, and depending on the round, and the intended purpose of the rifle, can have preferred performance.
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 ;)
You get what you pay for, and if you are wanting a basic rifle to plink with and teach your kids to shoot, for home defense if necessay, and capable of cost effective modular upgrades in the future, the $500 AR15 is where it's at..