Re: What's the most reliable AR you've ever owned?
I only ever owned one complete factory AR and it didn't stay in the factory configuration for long. I've built every AR I own from quality parts and have run some of these guns very, very hard. When I was selling suppressors I was performing demos frequently (several times a month and sometimes a couple times a week) and couldn't afford to have a gun go down during a demo. I maintain my ARs very well and HAVE experienced failures but nothing that I wouldn't chalk up to normal wear, the occasional bad ammo and maybe the occasional bad magazine.
I have one particular rifle with a Sabre barrel on it that has over 30K rounds through it. At the time I was also selling Sabre factory SBRs (in fact they didn't sell factory SBRs to the public until we talked them into it!) and one of the Sabre guys wanted me to get one gun I had to a documented 50K round count so they could check the barrel erosion. That gun was used for demo every week with a suppressor and it was a full-auto gun so it got a LOT of abuse. I'd let people shoot it as much as they wanted with their quality ammo.
I also used that gun to test suppressors. We helped do things like test the new AAC Blackout mount while it was still being developed. We destroyed a few older Phantom-style mounts and a couple suppressors in the process but the gun never failed.
Long story short, most AR failures I see at public ranges are attributable to one of several issues: user doesn't know how to properly clean/maintain the weapon, use of crap ammo, use of crap magazines, gun is made with cheap parts. YES, all parts are not created equal.
All my ARs are built with quality parts and are properly maintained. I stick to quality ammo and magazine. All this greatly increases the chances of having few failures.
Sorry for the pre-coffee ramblings.