Hunter 223, Most Colt barrels are chrome lined for durability. Certain police carbines and the 24" Delta Elite barrels are not chrome lined in order to improve accuracy. Colt is the sole source for the M4 and M4A1 carbines to the US military. They buy the components for the 4-position telestock assembly from subcontracters and put them through Colt quality control before assembly to assure MilSpec standards.
I agree Colt is the best I have experienced. I own a Colt 4 position collapsible and it is the nicest of all the others that I have personally used. I am sure there are other good ones, Bushmaster, etc but you can never go wrong with Colt. Best of luck to you!