I bought a used RRA AR-15.  I'm trying to find out anything about the barrel that I can.  The rifle was bought new by the first guy in Feb as a complete RRA rifle from an RRA dealer.  The lower and upper are both marked RRA, has RRA NM trigger, so I am assuming that the barrel is RRA, also.

It is 16" M4 profile, thicker under the handguards.  Has "M4" feedramps.  There is not a single thing stamped anywhere in front of the front sight.  Under the handguards, near the barrel nut, there is "N9A" stamped.  There is also a "1" stamped separate from the other stamping (also oriented differently).

Anything anyone could tell me would be great.  5.56?  Chrome-lined?  Twist?  

I saw a chart somewhere on this site before with barrel info, but I can't find it anymore.  I'll probably call RRA on Monday to see if they can help.

Thanks.

N = 5.56 chamber
9 = 1/9 twist
A = NOT chrome lined

FWIW, RRA adds ramps after the fact, with a fixture and grinder, likely a Dremel.  They aren't a standard option, using the "correct" equipment.  If done properly, they don't hurt anything, but I've seen some that looked less than ideal.

Good info from Mongo as usual. Yes the bbl is RRA as they dont mark them in front of the FSB.

Thanks Mongo.  Exactly what I needed to know.