I am thinking of building a light(er) weight ar.  Is their much weight to save starting/cost with a 20" a1 (pencil barrel) over a 16" (Dissipator).  Or is the big difference just the retro hand guard.  

Oh if I go with the a1, any advice/warnings on the carrier/bolt group.

I don't know about weight, but it feels much more handy.

I'd just go with a 14.5 with a pinned on Flash hider. You save another 1.5 inches.

It's a great weapon at that size. Go with a A1 upper and switch the front and rear sight to a2 standards.

Get some 20 round NHMTG mags as well.

If you've never fired a rifle of this size you'll be pleasently surprised.

It has just been to long since I fired my brothers a1 to remember - and then he had a clip on scope on it (should have just left it in the natural state - iron).  I have fired his tactical entry car, and it just does not feel right (but at least he had better choice in optics on that one).  I have a varmint and at roughly 12lbs it is no fun to lug around all day - but great for paper punching (I need to upgrade the optics on that one some day... - oh well).  

Of course this was all before that tragic boating accident.