Installing a YHM rail and wasn't sure how much to use- thanks in advance guys

I always just dab my finger in the grease and apply it lightly around the entire threaded area of the receiver.  Not real light and not thick, put the barrel nut on (just hand tight) and back it off for a time or two, then assemble it per spec.  I may not be applying the grease "properly" but it has worked for quite a few ARs.

-X

Very thin coat on the barrel extension and the surface of the socket in the upper receiver that fits the barrel extension.  A thick coat on both threads of the barrel nut and the upper receiver.  Work the grease back and forth and make sure it gets down into the threads, NOT so thick, you can still see the waves of the threads under the coat of grease.  Have a rag, it gets messy working it in.  A medium coat on the face of collar on the barrel and the barrel nut, that will clamp the barrel into the receiver, to reduce the friction as you tighten it down.

Thats what I did, it resulted in a bead of Moly grease right to the edge of gap at the back of the barrel nut, but NOT squishing out or getting on the receiver.