I'm very late to this thread, and I am not sure I am addressing the latest twist, however if I was looking for a single AR-15 that could be used for most everything I would select something along these lines:
It would be an A4 set up as a NM rifle. By this I mean that it would have a nice 20 inch stainless steel barrel with either 1:7 or 1:8 twist, in a flat top receiver with the NM carry handle and front sight. There would be a free float tube and the trigger would be a nice two stage NM trigger.
Armalite makes a very nice one called the M15 A4 SPRII National Match, for example.
You could use it right out of the box and then you could mount some type of optics by simply removing the carry handle. The 20 inch barrel will easily carry your bullets supersonically past 600 yards and if you handload, up to 1000 yards. The rifle will be very nice to shoot, highly accurate and if one day you get into a panic where you MUST have a 16 or shorter barrel, just swap the upper, the lower will have all the NM parts you need.
If you want to get it built from scratch, use that rifle as your prototype.
Last edited by FTR_Shooter; 07/21/09.
