The AR system is incredibly versatile. It can be built in any caliber up to small magnums, or down to .22lr. With the AR system, you can buy any quality AR, and in five minutes, (and with $300-$1500) you can change the thing into just about anything you want with a change of upper.
Right now I have a Bushmaster Superlight carbine, M4 and A2 stocks for it, plus rails and optics (pictured here all tarted up just for fun with the major accessories. I usualy take it out with a red dot and no bipod).
It has a 16" ultra thin profile barrel that smokes after 20 rounds; it's great for short range stuff, it'd be a decent entry gun, but it's not for long range work. At 50 yards its a tack driver. At up to 100 yards I can put an entire 30rd magazine into a 2" circle (minus a couple flyers). Anything more than 100 yds, and the groups open up considerably, no matter who's shooting it, up until the point at 200-300 yards (depending on the load) where it doesnt so much group as it does pattern.
Of course with a barrel that light, and that short, thats as good as I can reasonably expect. I like the thing in this config, because it only weighs 5lbs, not because it's super accurate.
But here's the thing, I dont have to settle for that. Without a gunsmith, without huge expense, and with almost no time at all, I can have a match rifle.
$200 gets me a drop-in match trigger, no major gunsmithing needed. When the money allows (about $600) I'm going to pick up a 24" ultra heavy barreled upper; probably a 1-in 7" 1" diameter stainless with a deeply recessed crown, and maybe a muzzlebreak (for the harmonics, not the recoil). Using 77-82gr match loads, and decent optics that can easily be a 600 yard gun for varmints or for punching holes in paper. If I were to buy a whole new match or varmint rifle, it would cost me two to three times that.
What about a practice weapon? $275 gets you a target quality .22lr or upper and magazine ($40 for each additional mag usually), that lets you practice with el cheapo .22, while retaining the same controls (and optics if you want) as your match and assault rifle. Oh and .223 is the ideal first centerfire rifle caliber to train people with (the main reason why it's so popular).
For those who hate the 5.56n for serious social purposes (and I'm not a huge fan myself) for $450-550 you can grab an upper in 7.62x39, opening you up to some of the cheapest and most easily available ammo. If you don't like the commie caliber, for about $550, you can grab a 6.8spc or 6.5 grendel upper; which, if the ammo ever gets to be more commonly available, should be great performers.
For the most fun, and around $1000-1500 there are a number of companies producing .50bmg uppers for the AR. Considering most .50bmg rifles sell for upwards of $2500, that's a pretty good deal, as long as you have a decent forged reciever (I'm not so sure about the cast ones standing up to a .50 for too long).
Hell, grab yourself one of those shotgun set cases (four foam sides, 36" long, designed to take four broken down shotguns), make cutouts for all your uppers, your lower, optics etc... (well, except the .50, which is HUGE) and get all mission impossible with the thing if you want.
The point is that the AR is a great system, versatile, reliable, accurate, lightweight and packable. Just remember, the AR is an assault rifle, not a battle rifle, and for non-social purposes it's a target and varmint gun, not a hunting gun . Use it for what it's good at, and you'll never be unhappy with it.
