Chrome was used because that was the best technology available at the time for making the bore stand up for full auto fire and keeping the bore from rusting and pitting in wet climate use. Nitriding aka Tennifer aka Melonite, etc. came along and was made popular by Glock and has since proven its worth. Nitriding hardens the barrel surface without plating problems so it can have better accuracy than a poorly made chromed barrel. It has nearly as long a life unless you like to do mag dumps in which case the chrome is supposed to last a bit longer (depending on the quality of the chrome plating btw), and is more resistant to rust, elements, fouling, etc, than plain chrome moly barrels.
Nitriding has been successful in the market place as it can involve just a slight premium over chrome moly versus a bit more for chromed bores or stainless steel. In essence, don't worry about the barrel, the other posters are right in that you will have to shoot a lot of ammo before you start keyholing rounds.
If it makes you feel better, go to ar15.com and look up the long running Battlefield Las Vegas thread aka Henderson Defense where a commercial gunrange operator reports on basically torture testing of ARs using full auto magdumps by customers (they rent packages for entertainment value where folks can shoot full auto). That thread will tell you most of what you need to know about the AR's reliability. Also believe that they have an AK thread that I have checked in the past.