“Milspec” is a sales buzzword that provides a loose definition of the minimum standard of quality for a specific dependable combat weapon. There are several brands that say they are milspec and are not even close to that minimum level of acceptable quality.
If you are buying a weapon for fun or for just plinking, anything will do. If your weapon is for work, home or self defense- you should look more closely at the options you are considering.
If a brand is providing weapons that don’t feature these examples they aren’t meeting “milspec”:
-milspec receiver extensions versus commercial
-auto bolt carrier group
-staked gas key and castle nut
Those are just some simple examples that are easily checked.
The combination of 1/7 twist and 5.56 chambers are set for specific types of military grade ammunition (m855 and m193 for example). If you plan on shooting light weight ammunition, 1/9 twist works fine. 1/8 provides a well rounded performance for various projectiles. Medium and longer/heavier projectiles work well with 1/7 twist.
A “milspec” carbine would use a carbine length gas system. Most people that know better prefer a midlength gas system in a carbine.
To make matters more complicated -commercially sold weapons are incapable of being the same spec as military grade weapons. There is a whole technical data package (tdp) associated with military production and it is tightly controlled.
FN’s military contract weapons have a completely separate production from their commercial line. This seperation is due to the military tdp not being allowed to be used in the commercial variants.
Recap- the term milspec is thrown around to sell to people who do not know better. Milspec is the minimum for quality for a specific type of rifle. There are better methods and means available, you just need to study to know what to look for.