On the Rock River Arms website/catalog, you can order their Varminter A4 with a couple of different options that I have questions about.  I'm new to the AR and don't know what options would best suit me.  Looking for the most range I can get and accuracy of course.  

1)They offer it with a 16, 18, 20, and 24 inch barrel.  I'm assuming the longer the barrel, the higher the velocity??  Does one better suit the .223?  ...or just go with the 24?

2)They offer the barrel on the 24 in either a 1:8 or 1:12 twist variant.  What's the difference?

Any help WILL be appreciated.

1.) 20" is about as long as you need an AR. Anything longer than that seems REALLY long and is better suited to bench shooting, not much walking. If you're going for that, or something like hunting out of the back of a pick-up (i.e., uncase the rifle, walk 8 feet to the back of the truck and lay down in the bed) 24" won't hinder you much.

2.) 1/8 twist will be good shooting anywhere from 40gr bullets to 80gr match bullets. 1/12 is geared towards the really light stuff. 62-64gr is said to be about the heaviest you can shoot out of a 1/12 twist barrel with good results.

Hope this helps a little.

WIZZO