The stock is among the worst parts of the AR to try to save weight. Weight towards the rear makes it balance better & will actually make the gun feel more nimble.
Be cognizant of barrel profile. Too heavy & you've built a pig. Too light & you'll sacrifice some measure of accuracy.
Lightweight bolt carriers can effect reliability.
My favorite weight cutting measures on AR builds are titanium gas blocks (I use V7 ion bonded or Battle Arms ion bonded) , a muzzle device not over 3oz (I like Rainier Arms flash hiders & the CMT CFC), and lightweight, free float handguards.