Colt is the only maker who uses 100% mil-spec standard parts in their commercial rifles like the LE6920.
As above, technically the Colt commercial rifles are not really "mi-spec" since they aren't US government issue rifles.
However, Colt doesn't run two supply chains or two production lines, one for commercial and one for military sales rifles.
They use the same parts in both, so if you buy, as example, a Colt LE6920 M4 carbine, you're getting a rifle with the same parts as used by the military full-auto rifles.
In effect, when Colt does the final assembly on a commercial M4 and a military M4, the exact same upper receiver, barrel, bolt, bolt carrier, etc are taken from the same stock and assembled to a lower.
The military lower will be a full auto, the commercial will be a semi-auto, but other than the full or semi parts, everything is the same.
With the possible exception of the new commercial FN made rifles, no other maker uses 100% mil-spec standard parts in their rifles.
Some builders may use some parts that are better then the military specification, but only in major parts like the bolt or bolt carrier.
In the Colt, EVERY screw, pin, stock, bolt, barrel, trigger, and every other part, no matter how minor is made to the mil-spec standard.
This doesn't necessarily mean the Colt is better than any other brand of rifle, but you do have some "yard stick" to measure them by
We know what the Colt is made of and that every part has to meet a standard.
With other brands you have to go on their word. Since they don't have to meet any standard other than their own, their rifles can have cheap parts made in China from soft metal with a painted finish. Point is you have no way of knowing other than what they tell you.
Colt also gives you their word about meeting mil-spec standards, but since they use exactly the same parts for all their standard rifles, and could be sued for fraud by telling you their rifles are made of mil-spec parts when they weren't, you have a standard you can measure them by.
Mil-spec means that whether Colt makes a pin or they buy it from a third party contractor, Colt MUST furnish to the government legally verifiable documentation that each and every part is made to that standard right down to heat treating and even the type and quality of finish.
When a contractor supplies a part to Colt, they have to include official lab tests and documentation that the part is made to the spec.
If they instead furnished some cheesy non-spec Chinese part, that would be a criminal offense.