Luck.
The AR system is like Legos for the big kids. A good barrel is essential.
A 20" will get you to MR/Medium Range/600yd without significant strain. I prefer 24" for that distance but that's just a hedge against unfavorable conditions. While many shoot the 223/5.56 considerably further than 600, I think that's a bit of a stretch, and prefer a 6.5mm for the LR/1000yd distances.
Moreover, the longer the barrel, the less extreme the necessary load, and likely, the better the barrel survives the process.
Good optics are also essential, and while I'm not personally familiar with that scope, it is a familiar name around here.
At distance, drop turns inconsistent velocities into vertical spread. If you handload, a good bullet and care about charge weight consistency will reduce that vertical spread. If you don't handload, and have a rifling twist of 9" or faster, the factory match loads with 75gr and/or 77gr bullets should be adequate. I suggest Hornady 75gr Steel Match, or the IMI 77gr Razor Core. I shoot them in the 24" with no issues, and make no predictions about 20".
Greg