Re: Ar10 barrel nut shim
What are you torquing it to? Several different styles out there, so some pics may help. Many of them are just a bit different, but you should be able to torque the nut far enough to get one of the holes lined uop with the gas tube hole in the upper. Use an alignment tool to verify this, but that's where you want it to be.
And no, there shouldn't be any shims involved in this.