Specs and inspection standards are always an interesting issue. I have worked for a government supplier, who was required to document each step of construction, in which a worker initialed off the work was done to standard. And a government inspector was on site checking, and they would fail a lot on occasion. For a hundred piece lot, there could be anywhere from 15 to 50 pages of documentation.
Said documentation accompanies the lot to it's first distribution point. In the case of the M16 and M4, that is handled by the receiving location under Tank and Armament Command, who inspects the weapons and paperwork, then signs off as being compliant to standard.
Technically, until that is done, it's not milspec, and only US Govern't guns accepted for service are. All others are not, even if made with the identical parts. No paperwork, it didn't happen, and it's not official unless accepts. Military spec requires government acceptance as the result.
On the open market, we buy the seller, and do that by judging from their text in ads, the maturity of their marketing image, and their ability to sell firearms that are accepted under government standards.
So, Colt, FN, Remington, Bushmaster, LWRC, and a few others are "milspec" providers. Nonetheless, someone could assemble or purchase a Noveske, BCM, Armalite, or half a dozen others and have a better gun, more reliable, tougher, more accurate, and more ergonomic with the proper accessories. The Marines use the Norgon ambi control, the Army, not so much.
In general, the leading "best practices" for making a firearm are often more expensive, and are not used unless required by the TDP, milspec, or are just cheaper, which isn't often. Therefore, what gets bid for contract is often the lowest possible cost expense for the manufacturer. They don't gild the lily with CNC billet lowers or Noveske keymod rails. Even Colt doesn't own a forge, they buy the platters from one and machine the lowers and upper from them. I seriously speculate that a lot of smaller parts aren't made in house either - springs, screws, etc. are expensive to make on a contract basis in house, and the existence of a lot of the manufacturing base outside the company walls of a lot of makers is evidence. In fact, there are very few who advertise that they make the entire rifle right down to the last screw. What you do hear is that they have the highest quality, tho, and it's always in serious prose with no fooling around. If they refer to the user base and it's professionalism, they don't indulge in popular catch words and keep it oblique.
I haven't seen an HK ad with their gun and Osama's last photo op proclaiming they are the Gun That Rules Them All. On the other hand, there was a lot of personal bragging from a highly placed government official taking the credit for the kill. . . .
So, the rule is the trashier and more jingoistic the ad, the less likely that maker actually puts out a product that is gov't spec. They are selling a lot of sizzle to hide the fact their steak isn't all that. It's marketing 101, if you aren't all that, dazzle them and baffle them.
It really is a matter of interpreting nuance and reading between the lines. It takes some skills on the internet in reading comprehension and understanding the source that information is coming from.
I will say it, tho, that even a qualified and experienced user will get it wrong. They are not a firearms designer - User 1 didn't make the machine, and no amount of bluster on a forum guarantees they have a complete understanding of it's dynamic cycling. They didn't do the gas pressure analysis, don't work in a plant making them, and didn't come up with a lot of the modifications. In most cases, they weren't even born when it was invented. Be very careful taking away any more from it than what their subject matter expertise has taught them - like a MD who spends half his week on construction projects, having an opinion and forcefully expressing it doesn't make them an engineer.
Therefore, listen carefully and double check facts before accepting them. If everything that was said on the internet was true, then it would be an interesting world indeed.
