I have a few AR's. 3 are 5.56/.223, .308, and one is a .243 WSSM (for sale
). Here are the configurations;
-Bushy Varminter 5.56/.223 with a 24" barrel
-Home built 16" carbine in 5.56
-Cheap DSA Arms 16" carbine upper with home built lower
-DPMS AP4 in .308 w/16" barrel
-Oly Arms .243 WSSM with a 20" 1:8 twist barrel
I have found so far that for the most part, my 16" home brew is more accurate than my 24" Bushy. My AP4 is also a very accurate shooter with handloads and match bullets). My .243 WSSM is also a great shooter (handloads of course), but it also has a heavy barrel which is very stiff.
So really, barrel length has absolutely nothing to do with accuracy. It will effect velocity, but that's it. If you are shooting open sights, then the longer sight radius of a longer barrel would be an advantage. But as one member posted already, throw optics on, and that rule goes out the window.
If I were to build a dedicated hunting rig in 5.56, I would choose a medium to "lighter" weight contour in an 18" ss barrel with a 1:8 twist. Also, on twist, 1:8 will shoot the heavy stuff all the way down to the light stuff just fine.
There was actually an article in shooting times or one of those magazines about this very subject. They test various rifles with different twists and a multitude of bullet styles and weights. Even a 1:7 was good to go with the 45 grainers!
Here is my home built 16" 5.56. I absolutely love the way it shoots and handles. It's light and easy to maneuver.