I would say the first 3 mods to drop weight are barrel, handguard and stock. Depending on what range your plinking and varmint hunting, either go with a slimmer profile barrel or go with a shorter barrel with same profile. Handguard choices could be slick carbon fiber tube, shorter handguard or slim profile with all excess material removed (KMR, ALG, Clark Custom, Carbon Arms, 2A, etc). Last would be the stock, if you're running a one of the heavy weights (UBR, PRS, etc) and you don't find yourself using any adjustment, ditch it and go with a MFT, BCM, Moe-SL, Super-Stoc. If you do need the adjustment then check out the Luth-AR or XLR.