I am no expert in the carbine field by any means, but I have used on in combat before and here area few points that I swear by.
-The bolt needs to be wet
-Zero irons to same POA/POI as your RDS and buy a quality RDS and irons. I like a 300yd zero, it is easy to wing it for shorter/longer distances. (EOtech or Aimpoint) If you buy a Barska or Tasco you are doing it wrong
-Use P-mags. The feed lips break before they bend. They either work 100% or not at all. With metal mags, the lips can bend, they may work, they may not, it is hard to tell by looking at them. With a P-mag, a quick look can determine seviceability
-A quality sling makes all the difference. But if it says blackhawk on it you are doing it wrong
-Trigger control is vital for success. You will be amazed at the speed and accuracy, even with a less than perfect sight alignment/picture, you can get with excellent trigger control.
-and for goodness sake, do not hang $10k in gay accessories off the damn thing. BUIS, RDS, rail, maybe a forward grip, and maybe a light and that is it (please no bayonet)
-Oh, and if your rifle says bushmaster or DPMS you are doing it wrong