I recently finished a build that I called lightweight. Until I saw some of the crazy light configurations posted in this thread.
Can't imagine how those feel. Mine is about 7.5 lbs with everything it would walk around with except the magazine (I haven't weighed it completed, yet) and the people who have handled it all comment how light it is, or ask if the internals are present.
I'm starting to think someone specifically selling extremely lightweight AR-15 components could do well for themselves...

