My first build was intended to be fairly lightweight, and while it certainly isn't the lightest option (certainly also not the heaviest), I went with the Geissele Mk 16 and I'm pretty pleased with it, although I went with a shorter length than what most of y'all use for 16" rifles (10.5") for my own reasons (of which less weight was the least important). With an empty 30-round magazine and two sling swivels installed, it weighs 6 lbs. 9.5 oz. Without the magazine or swivels, it weighs 6 lbs. 4.5 oz. I went with a pencil barrel, titanium lo-pro gas block, no-FA upper, and ALG swivels as part of trying to limit weight. I had considered getting titanium parts for a number of the smaller parts, but I'd save only a little over 2 oz. at over $100 in cost, so I didn't bother with it I also went with the LWRC compact stock so I could have the cheek rest of SOPMOD stocks but without the weight. There are lighter options, of course, but these stocks aren't heavy. For everything else, I just went with what I wanted without necessarily considering weight, but most of the major weight sources are already accounted for after the above.