Question for Constructor (or anyone else)

[La26]

I saw a previous thread where you stated you use Mobil 1 for lube on the AR-15. I went to the local Auto store, and there were several weights of Mobil 1. They had 5w-30, 20w-50, and a 40w something????

Which would you recommnd for the AR-15.

[Constructor]

Anything works but I use the 5W-30, same stuff that I use in our car.