For an AR, I would prefer stainless instead of cm. I have a RRA Varmiter with the 24" Stainless match barrel, it will shoot sub 1/2" over & over. If you follow the match shooters & those who buy AR's for Tar/Var chores, the prefered barrel is a match grade stainless. The
chrome lined bores do have their place & they excell for extended rapid fire, combat situations, they are not as damaged from excessive heat. So, in Mil. applications the chrome lined is better & they can be highly accurate, but for BEST Accuracy & good life for relatively rapid fire, stainless is prefered by most. It is noteworthy though that Bushmaster does use ch. lined in some accurate AR's. Go to the sites of the other leading AR Companies & look at what type of barrels they use for he precision versions. BTW, RRA guarantees 3/4". Other more expensive AR's like the Les Baer use stainless & Les Guar. 1/2". Go to a custom builder like D-Tech & I believe you will hear stainless all the way. But all 3 can be great.