I think there's a lot of misunderstanding about the SR15E3. This post by Trey Knight is about a decade old, but I think it offers a lot of insight into what's behind the rifle's design.
Any gun is as good as the weakest part of that gun. Cost has to be factored in . If a gun costs 3 times as much as another but lasts only twice as long is it better. The biggest problem with the entire M4 world is that gun is a compromise. The gun and round (M855) were originally designed around a 18" bbl platform. The gas system,buffer tube bolt, everything. When we compromised the design by hacking off the bbl and buffer tube things got funny. We(industry) have been trying to fix this compromise of Stoner's design since it occurred. We have tried boosters,buffers,rubber bumpers, rocket wire extractor springs, pistons, dual extractor springs, you name it. Most of the developments that became the M4 actually came out of a tanker gun program. The M4 was about as right as we could get it at the time. For procurement logistics and other reasons the design was frozen at this point. Can we (industry) make a better gun than a M4? Perhaps but probably not for the same dollar and 100% parts commonality. As I stated a gun is as good as its weakest link and the weakest link in 16" and under short gas system guns is the extractor . I would say it is a 3000 round life cycle. If I can change this $5 part on schedule then there should not be a problem. If I can't then that $5 part could cause my entire rifle to be useless and as a soldier or someone else who depends on their rifle this way this $5 part could cost them their life. The next point of failure would perhaps be the bolt. I'm not going to quote life cycle here because it is a not totally agreed on subject but with suppressor use it is certainly more limited. Last is the bbl. A hammer forged chrome lined bbl is going to last longer than other types of bbls. It may or may not be as accurate but when improperly maintained a HF CL bbl will beat out all others period. I am going to call the life cycle of a good HF CL bbl to be 20,000 rounds. There are certainly reports of them lasting shorter under heavier firing schedules, and it won't explode at this point but the accuracy will start to deteriorate at this point.
KAC has tried to build a rifle that all the parts will last the full 20,000 rounds. Zero parts replacement. The downside is it costs more and lack of parts compatibility .
The bottom line as I have said before the Mil spec requirement is certainly there for a reason. It is possible to build a gun that will perform better than a mil-spec gun that may not meet the requirement. Many people claiming Mil-spec may not actually meet that requirement for something as obscure as ISO certification.
There are so many good choices out there in the AR world. So many good companies doing innovative stuff. I would hate to see industry not advance the AR design because we are held to trying to just build mil-spec guns.
At what point does a gun not become an AR anymore? We all know that the non-full curve magazine is a weak link. Would you guys be willing to throw all your mags away in order to achieve a higher level of reliability? We (US gov't) were not willing to take that step with the SCAR.
Just some thoughts ;sorry for a rambling post , it is not meant to be a rant.