@ Raz - get-um while congress is on vacation!
Not a bad deal these days, at Target Sports USA
Federal 5.56mm XM855 NATO 62 Grain FMJ 420 rds on Stripper Clips in Ammo Can
Special $210.00
FREE SHIPPING INCLUDED
My rifle has a slow twist (1:9), so the higher price for the heavier bullet doesn't buy me anything. I stock up when I get the 55gr at around $0.40@. My next such rifle will have a faster twist and a longer barrel.
Just re-barrel it.
But then I don't have an excuse to buy another gun.
But you don't have the money for a new AR anyway so just what difference does it make at this time?
I thought "hunting rifle" was next on the list... not that you couldn't hunt with another AR. Does he already have a .308? 
Oh, and I'm not terribly interested in a .308.
You were not interested in a full size .40 either so you bought two.
I didn't say I wasn't interested in it, only that I didn't NEED it.
I don't need a .308, but I'm also not particularly interested in that cartridge.
A .308 is a fundamental member of every Murican arsenal.
Used to be. It's outdated technology now.
Wonder why they still sell so many of them in modern rifles 
Same reason they still sell so many 1911's in 45acp. Tradition, heritage, aesthetics, and personal preference. A 308 will get the job done, just not something I'm personally exercised about. Personal preference.
And BTW, I can afford whatever I decide is important to me. The 308 just isn't that important to me right now. But that could change tomorrow, just like it did last week for a couple of FNS-40's.