Hey JB, in building an ar15, the heaviest components are the barrel, upper and lower receivers, bolt carrier, buffer, butt stock configuration, steel front sight base. The things that are available in a lighter version are the barrel, and there is a consideral difference in lengths chosen, 16 vs 18 vs 20 inch, all other dimensions being equal. For my very light but reliable, yet accurate rifle, I would use the following.
1. Lothar Walther 16 in. very light stainless barrel, 199.00 factory direct.
2. A3 upper, standard lower, I like DPMS, but there are many quality units available.
3. An alloy gas manifold, low profile, if a front sight is not important, I like JP.
4. A CAR15 butt stock, standard milspec, there are better, but it's adequate and light.
5. DPMS quad rail, carbine length full float tube, good quality and very reasonable cost.
6. Enodine or Brownell hydraulic buffer, less recoil and spring noise.
There are titanium bolt carriers, high dollar, lighter receivers, alloy high dollar, polymer, not proven enough yet. Standard flash hiders are light, but muzzle brakes aren't.
Hope this helps.
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