All my parts will be in by Thursday for my 1st build.  Do you apply any grease to the barrel extension itself before you slide it into the upper reciever or install dry?

Thanks!

No need to grease the barrel extension.  The only purpose of using moly grease during assembly is to prevent corrosion between the barrel nut and the receiver.  I haven't heard of any problems with corrosion between the barrel extension and the receiver.  But it certianly wouldn't hurt anything so if it makes you feel better......why not!

I put a light film of Tetra Gun grease on the barrel extension and the barrel nut and receiver threads.
Does it help?
I haven't had problems installing a barrel when everything is prepped this way and I haven't had to resort to a three foot cheater pipe to get a barrel assembly apart when prepped this way either.

Yeah, I would do it.

Thanks,  I have some moly grease-I will put a film of that on the extension.

I don't feel the need to grease the extension.  Every one that I've taken down has always had some residue of gun oil from lubing.

Use a little of your anti-seize of choice before you put the barrel in. A little on the barrel nut threads might not hurt either.

Does the grease really stay put after shooting thousands of rounds?  I helped a friend take the barrel off an old M16A1 upper and what was left of grease looked more like carbon like one would find under their flash suppressor threads.

To the OP, it certainly shouldn't hurt anything by greasing it.

Years of use in the environment of a firearm, that can vary drastically on how the owner uses and cleans it, it would NOT be surprising to find all the grease gone, or the grease still there.  In cars, in my experience, even when you can't see any grease there anymore, whether some is there are not, it did its job preventing corrosion and seizing far better than putting things together dry.

I say do what the TM says, I can't remember what that is, if the TM is silent on the issue, then I would put a thin film of grease on the extension, it would NOT hurt and could help.

Anti-Seize would work, might even do better, just consider NOT mixing anti-seize with grease on the barrel nut threads.  Mixing lubes can give unexpected results, like they are incompatible and will break each other down, leaving you with less protection.  Pick one or the other for the threads and don't mix the lubes together.

I alway's use some anti seize. Some folk's and Smith's locktite. I always have looked at ease of removing, others want shit to stay put.

 I've never had problems in all these years with accuracy or things loosning up. I'll usually tighten and loosen a barrel nut 2-3 times before I torque it down for good.