There's part of the answer... Is that the video where they were shooting with iron sights or an unmagnified dot? An AR is capable of outshooting its factory iron sights; to really see what the respective platforms can do, fit them with good magnified optics to reduce aiming error, and then compare groups at 200+ yards. One of the draws of the AR is that it offers bolt-action accuracy in a semiauto platform. An AR with a quality barrel and a free-float tube will outshoot almost any other semiauto on the market, as well as a whole lot of bolt-actions. A decent AR, set up properly, is extremly reliable. You can get them to fail by tuning them for very hot loads only (H2, H3 buffer, heavier springs) and then shooting light loads, or by underlubricating the gun and then running it without lube or cleaning for thousands of rounds, or by using crappy magazines, or by overgassing/undergassing them via mismatching components. But a good AR will run well even if barely maintained (e.g., squirting oil into the gas vent holes every once in a while and calling it good). http://www.thefirearmblog.com/blog/2010/06/09/a-clean-wouldnt-hurt/ .223/5.56mm isn't ballistically inferior to 5.45x39mm in general. A very good 5.45 load will outperform a mediocre 5.56mm load, but the best 5.56mm loads will outperform the best 5.45mm loads at long range. Compare the 77 grain Sierra MatchKing loads in .223/5.56mm to any 5.45mm load at 500+ yards, for example. The very best loads for long range shooting are pricey, though. Ergonomics, ease of customization, accuracy, reliability, value, and versatility. It is not the only good choice by any means (I do like AK's, and the AUG, and others), but there are very, very few centerfire semiautos for $600-$1000 that will match an AR in all those categories, and it is also a very reasonable choice for HD (given appropriate ammo selection).