Those wishing to become a "super duper sniper" should consider another platform IMO. You can pretty well with an AR. You can do great with a bol action rifle or possibly a really good semi-auto. But for the most part long range shooting is done with bolt action rifles. I realize a person can build an AR to shoot long distances but it will cost far more than a bolt action that will shoot the same distance.

There used to be a 500 yard range at the gun club I was in. I went there to shoot pretty often. I shot quite a few AR's including some AR-10's at that range. I also shot my Savage 12 LRPV .223. I could generally shoot minute of man with the AR's including the 10. I shot 5" groups with the LRPV. And the wind affected the accuracy. With a .308 rifle of the same design or similar it should be possible to cut down that 5" group size.

I love my AR. It's a great rifle in many ways including accuracy. But it doesn't compare to a purpose built long range rifle in terms of accuracy at 500 yards.