lengths

What barrel length is anyone using on their AR uppers to get out to 600yds (using 77gr ammo) accurately and consistently? Would a 16" do the job or does it need to be longer? Thanks for your help.

im going to get an AR when funds approve, and i want to make the most informed decision possible, my question is about the differences in gas system length. like carbine mid and rifle is one more reliable, durable, etc? thanks in advance

Most if the 6.5x47 handload threads concentrate on grains of powder and velocity. I'm still working with my gunsmith to come up with the optimum throat length for the Lapua 123/139 and Berger 130 bullets. Many of you have suggested 0.109 freebore but I don't know what COAL and, more importantly...