The general "milspec" only describes what the items need to do (without specifying how it is made), what it looks like and other "milspec" the item needs to be in compliance with regarding manufacturing, quality control and packaging - and finally the drawings themselves.
See, if you don't test fire your rifle with M855 that is not made according to its own "milspec" using the testing protocol specified it is not US milspec.......some of the "MILSPEC" are not very useful or applicable to the commercial market.
Another example, the most common thing that got beaten to death is the staking of the gas key. There is a commonly used staking method used by Colt, but the milspec only said something about the "displayed" materials could not be squeezed over by so much vertically by the staking. In this case, you probably want to trust Colt because it has been doing this for 50 years but it is probably not "milspec" - just a common practice adopted by someone who has the most experience.