Yeah, I agree for sure, on the rifle round being more effective than a 9mm in the absolute........................but since 99% of those carrying daily are using handguns, I think we can surmise that the handgun round is "sufficient" for the most part, whatever that means, for short term, short range encounters.
If I know or think something more than that is going to be on the menu, then I'm going to pick a longer gun anyway.
So for me, average Joe Schmo, the 10.5" AR just doesn't have much real appeal, other than a novelty, hence the right bullet for it is kind moot.
And so I just use in my 14.7" gun, what I use in my 16 & 18" guns & don't give it much worry.
MM
If we're only talking about 5.56 in short ARs, I'd agree with you; I don't have much use for a shorty 5.56 myself. But the conversation changes a bit when the other available cartridges are thrown into the mix. With the 300 Blk for example, the question really becomes more about why to use a longer barrel and "what do I gain", to which the answer is "very little"; it just makes more sense to use a short 9"-10.5" barrel. Or with something like my 12.5" 6.5 Grendel, I acknowledge the compromises from a longer barrel, but it still is more effective downrange than my 16" 5.56, and is a lot easier to handle in tight spaces so it really does make a lot of sense.
Obviously you give up some ballistics in most rounds with a shorter barrel, but what you gain in maneuverability, general handiness, and ease of transport can be worth a lot too. Also - don't assume that a short barrel has to be limited to short range. Appropriate optics on something like my Grendel mentioned above make it effective a lot farther out than most people use their 16' carbines.
