I'm planning on ordering an upper to finish my first build soon and I was wondering how much of a difference in accuracy there is between the 16 inch and the 20 inch barrels? I plan on going with one of three barrels, the M4 style 16 inch, the HBAR style heavy 16 inch, or a heavy 20 inch. I plan on doing most of my shooting within 200 yards, with magnified optics, and standard ammo (no match grade ammo anyway). I dont need 1 moa accuracy, but it would be nice to be able to hit a groundhog at 100 yards. Any opinions on what barrel type and length to go with?