I've been doing various shooting with 14.5, 16, 18" when all sighted in at 100 yards. Bullet drop seems similar at 330 yards (my max range where i target practice.) If anything the ammo matters more. I found that old PMC 62 grain green tip 5.56 had less drop than Fiocchi 40 gr vmax 223 out of a 16" barrel. That was surprising.