Well, more than worrying about barrel length, I'd worry about optics. With just the irons, I had little ability to positively ID targets beyond 100-150m. When shooting at visible targets offhand from 300-400m I was able to hit a car sized area with ease--but I wouldn't have been able to see someone down there unless he was a total moron that didn't bother to use concealment or camoflage. While 5.56 ammo out of a 16" bbl is not ideal beyond 200m or so, it'll get the job done if you hit what needs hitting. No cartridge will do the job if you can't identify the target and send lead his way.
Crap, I KNEW I was too good-lookin' to not wear a mask. I think I'm going to have to grow a mustache and/or beard.
It seems that you are attracted to my beautifulness and automatically assume I'm a woman, though if you saw my performance when it comes to cleaning, laundry, and other womanly tasks you'd realize in a heartbeat I'm not a woman.