I previously owned the standard Sr 556 but got rid of it for a couple of reasons. One, I felt that it was a little "heavy" for an AR platform; and two, someone offered me ridiculous money for it (this was during the "scare" a few years back). I always told myself that the next Ruger SR 556 I bought would be the carbine model. I like the fact that Ruger fluted the barrel and integrated the flash hider into the barrel to save weight (and length). I just recently purchased the model 5913. That's the carbine version with all the bells and whistles of the standard model but includes the lightweight rail instead of the full picatinny on all sides. I couldn't be happier. Since I've owned both I can say from experience that the SR 556 CLA model is my favorite. If you prefer the permanent rails and don't mind a smidge of extra weight the carbine model will suit you just fine.
I took the gun out and shot 200 rounds of different ammo and it performed better than expected.i didn't experience any jams with the brass cased ammo.The only time it failed to feed is with some Tula ammo that I bought 5+ years ago.I put a different magazine in and the ammo functioned fine afterwards.The gun itself was accurate out of the box.I was hitting 2 and 3 inch groups at 100 yards while free standing with the sights that came with the gun.All in all I'm real happy with this gun