"Tight tolerances" is another internet myth.
What most people describe as tight tolerances don't exist in the way that is accurately used in manufacture or design. The "tight tolerances" of the AR are the blueprint specifications that the industry uses to get parts made that work together without hand fitting - or even being made in the same country. I have an lower machined in Arizona, an upper from Utah, and they accept parts from many other states. Yet, they all fit and the gun works, without one adjustment. It's the precise reason the Winchester 70 was redesigned, to eliminate hand labor.
Clearances are something else entirely, the working space deliberately left between parts to allow motion, like the .0035 clearance on engine bearing and the crankshaft journals. M16 clearances are NOT exceptionally tighter than other guns. If anything, military rifles tend to have more space between working parts, and are designed to tolerate it more, because they have to operate with more debris and contaminants in them.
Compare a Remington 700 bolt in it's guideways in the receiver, and an AR15 bolt in it's upper. The AR is far looser and literally can rattle if the action spring is removed, and the buffer does, regardless. The Remington bolt is much more tightly controlled. Same for the upper and lower, a well used M16 will literally wobble between them, the pins unable to prevent literal shaking of the upper. But, it can and will shoot just as accurately as ever.
A civilian gun would be scheduled for a trip to the gunsmith, or left hanging on the wall as economically unrepairable. The reason military guns tolerate it is in the design - the exceptional looseness has nothing to do with it's integrity.
AR's AREN'T victims to tight tolerances, they benefit from them, and so do those who assemble them from parts made all over the US. The clearances are something else entirely different - and keep it running with just a little lube through literally tens of thousands of rounds.
Shake, rattle, and roll, the AR15 isn't all that tight, but shoots that way, which confounds a lot of people unfamiliar with military weapons or their purpose.