I am 1 piece away from getting everything I need to build my first AR build. What buffer tube weight do I use? Not sure what is needed as far as info so I will tell you what I can. Here is a little about the build. 16 inch barrel, mid length gas system, spikes tactical BCG 5.56(nickle boron), Collapsible 6 position stock(YES, its going on a Pre ban). Do I want a H(3.9)? or lighter(2.8)? INFO would be appreciated very much, thank you! Chime in oh great AR gurus!