Originally Posted by xdm11chad
If anyone wants to throw in a suggestion on a upper I will use this for killing beer cans and other things down on the river or on my land looking to shoot 500 yards at least.
Sounds like you're not really after the lighter/faster/shorter design. You can
shoot 500+yds with almost any common AR and even with 55gr ball...but most of the more common designs are going to require a fair amount of compensation (not to mention skill and patience) for bullet drop beyond the first 300yds or so.
Ultimately step one is probably to select the ammunition that will acheive your desired results. Consider the range in question, ballistic coefficient, cost you're willing to spend per round, rate of fire, etc. Knowing what rounds you're going to shoot will point you in the right direction toward choosing the barrel design (length, density, and material) that will match it.
If you're after a precise "long range only" AR, a 1:7 or 1:8 twist rate will probably serve you best with the bullets that excel at those ranges. You may want a longer barrel, you may want a thicker (or maybe even stainless) barrel as well. And getting a decent trigger setup would also probably be a great benefit.
I think 1:8 twist is a vastly underutilized option. You could make a pretty good case that it's actually the most versatile and practical option for many AR platforms.