I don't think many "factory" AR barrels are made by the same company that sells them.
I don't think many "AR barrel makers", actually make barrels.
The huge majority of them buy barrel blanks from a small handful of actual makers. All of those makers are capable of producing excellent barrels. For the right price.
It comes down to how much the AR "manufacturer" or "barrel maker" is wanting to pay for their barrels. From the guys that actually do make them.
So "factory", "aftermarket", it's pretty much the same thing in this market. With a few exceptions for the really big makers, who all make many types of firearms and have their own high volume barrel making capacity.
It actually kinda bothers me how the term "barrel maker" gets used in the AR space. Guys apply that term to anyone that buys a blank and does some machining on it to fit it to an upper. That guy doesn't make barrels. Having bought custom barrels directly from guys who actually make barrels for many years for bolt guns, it just bothers me how anyone that actually buys barrels from someone else is a "barrel maker". The vasty majority of them ain't no such thing.
- DAA