First off, thanks for looking as always

I am in the middle of rebarreling my Colt MT6400C with an LE6920 barrel. Never in my life have I come across a barrel nut that was so damned tight. Can/should heat be applied to the nut to break it free, or should I just use a larger breaker bar and get medieval on it? Penetrating oil left overnight perhaps?

Thanks in advance for your help! At this point I'm putting over 100 lb/ft of torque on it and it hasn't moved so much as a millimeter.

Don't apply heat.  In this case, aluminum is on the inside, steel on the outside.  Aluminum (upper rx threaded area) has a higher thermal expansion rate than steel (the nut), so heat will make it tighter.

If anything, toss it in the deep freeze for an hour.

USE AN ACTION BLOCK, and make darn sure you use the insert.  If no insert, put in the bolt carrier without the bolt.

Use a cheater pipe on the breaker bar, or a long breaker bar.

Back to applying heat.  In the case of the buffer tube, the steel is on the inside, aluminum (the receiver) is on the outside.  The aluminum will expand away from the steel, as it has a higher thermal expansion rate.  A little heat here will aid a stubborn buffer tube.

You might try hosing it down in kroil and letting it sit overnight, can't hurt.

Colt does install their barrels pretty tight, same with Bushmasters.

Spray on some WD40, wait an hour or so, goto work with the cheater bar.


Good luck.

Thanks guys! I do use a good action block, so the upper is pretty well protected.

At the moment the upper is sitting upside down on the workbench doused with liquid wrench. I'll try it again tomorrow. If that doesn't work I'll clear out the freezer and go that route-my wife will love that...

My frustration just "cost" me one of my new Colt stripped upper receivers After banging my head against the wall with this I decided to simply mount the barrel to a new receiver for the moment, instead of worrying about rebarreling the other one.

I have the parts to build several of these 'poor mans' 6920s and 6020HBs anyway, so it doesn't really make a difference which barrel goes on what. At least I'll have something to shoot tomorrow, and then I can worry about removing this stubborn nut.

Thanks again for your help guys. It's nice to know that even at 1:00am I can get a question answered  

What recently worked for me was letting it soak in liquid wrench for several days, then use a torch to heat the nut while the receiver is dunked in an ice bucket.  Leave the receiver in the ice bucket for a minute after removing the heat from the barrel nut.

Try tapping the barrel nut wrench handle with a hammer.  Just don't tap too hard.

Try taking it to an armorer? Sorry.

Quoted: Try taking it to an armorer? Sorry.

Heh

It's done-soaking it with liquid wrench overnight was the ticket. The project is tentatively complete, here are before and after pics:

Postban with staked MagPul, ARMS #40, and Feinstein comp


Post sunset with Vltor, Troy BUIS, and LE6920 upper


Speaking of armorers, I called and asked one of my coworkers over the weekend for advice (I work for SigArms here in Exeter as a QA technician). His suggestion was to use a cutting torch to turn all of my "POS" ARs into razor blades As you might imagine, I get a mile high ration of shit for being an AR freak while employed by one of their competitors. A couple years ago the guys gave me a plastic M-16 with the word "Mattel" emblazoned with black Sharpie pen for Christmas.

Totally proper rig.  Your carbine Kung-fu is strong.

As soon as they have some nice 550's and 551's for sale under $1k, then they can talk about your ar's, until then...

Looks Great CJ!!!!!!

Quoted: As soon as they have some nice 550's and 551's for sale under $1k, then they can talk about your ar's, until then...

Kinda what I was thinking.......

+1 on the 550s

I just recently had the barrel off my BM to send off for threading.  It wasn't too bad.  I am a former mechanic and still do quite a bit of heavier work so the WMDs of the tool world were close at hand for me.  I did pretty much destroy the top of the bench where the vise was.  Both came with the house.  The bench top is particle board that looks like it been around a while, just hadn't got that far down the list yet.  Any way, it looked as though there was loc-tite on my barrel threads.  Possibly even the red variety.  Anyone else seen this>

Jester

There is NEVER any reason to use locktite on the barrel nut.