The AAC barrels are treated much the same as the new Army XM-2010 sniper rifle.
http://www.usatoday.com/news/militar...per09_ST_N.htm
I am not sure what heat-exposure concerns you have, but the nitriding-treatment is a benefit. Glock, HK and Swiss Arms does it to their barrels.
There is no saying how the AAC barrels compare to any specific custom barrel without shooting many samples of each and taking measurements to see which is more in spec. That being said, we already did that work. The AAC barrel is made to a very high standard.