Was thinking about trying to square the receiver on a few of my budget builds.  I saw a thread around here but can't find it that outlined how to use loc-tite purple to bed a barrel to the receiver.  Figured if I was going to tear them down that far I might as well experiment with this.

Can anyone point me to the thread or tell me the process?
Thx

I dont know about using purple loc-tite but I have been told to use red loc-tite on the outer surface of the barrel extension so to bed and solidify the mating to the upper receiver.  I have not done this but I have lapped/trued the faces of all of the upper receivers I own, some needed it more than others.  Its not like you are using epoxy to bed it, it any case it shouldnt take much more than a little heat from a propane torch to loosen the barrel from the upper receiver if you needed to service your rifle.

I've have never used loc-tite before but I would think the heat around the chamber/extension would eventually cook off most loc-tite products but I'm no expert on that. I guess you could go with something like rockset that is way more heat resistant than loc-tite if you really felt the need to try and "bed" the barrel to the upper but I personally think squaring/lapping the upper face before the barrel is installed then torquing the barrel nut correctly is way more important than using any bedding on it but that's just my opinion.

I use RC 620 for certain builds.  I think it's the correct compound since it's designed to fill gaps between slip fit cylinders which is exactly what an extension to receiver is.  A worn barrel can be pressed off if necessary.

http://www.midwayusa.com/viewproduct/?productnumber=171860

RockSet

Not super strong, so it will be easy to remove the barrel later, but VERY temp resistant.  Something like 1500 degrees.  You will not need heat to break it loose.

That seems unnecessary.  If you torque the barrel nut and put the gas tube between the teeth you should be GTG.

I knew there was a specific type of loctite for a press fit. I am going to try some on a large to small spin adapter. There is also a green, gunsmith grade, loctite for small screws.

If you use loctite, and get the barrel too hot, it will cook away.  And the barrel can easily get too hot for loctite.

Read this thread (especially posts by rcw3)

AR accurizing

As per that thread, I use blue loctite, as it does a great job and you can still get the receiver/barrel apart without any trouble you just have to tap the upper off the barrel with a rubber mallet.  High temp RTV compound works good as well.

As for the loctite melting, cooking off, boiling or whatever - utter nonsense; loctite doesn't work like that. Heat affects its ability to maintain its shear strength (as in how much force you need to get it off a fastner for instance) - but it doesn't become runny or anything, or otherwise disappear (it turns to a white film) - especially when using it in the confines of a barrel extension, where even if there were lots of heat, it would still continue to be effective in doing its job of making the barrel/upper fit very snug.  

And on the subject of excessive heat in the barrel extension......wrong.  The heat is generated in front of that.  I have taken apart two loctited barrel/receivers now, and on both, the loctite was observed to have remained firmly in place and still retaining its blue color.  If it had been excessively heated, it would be whiter (but even then still working in this type of application).

As to whether this is a good idea or not - IMO it is.  I once had a barrel which for no reason I could figure, would string shots as it heated up.  Torque etc was perfect.  I followed the loctite advise, and lo and behold....no more vertical stringing.  Hope that all helps.

Edit again - loctite will not "square" your upper - for that you'll need a lapping tool (as sold by Brownells, for instance).  But even without doing that, the loctite will relieve any pressure points with the barrel that might be caused as it effectively makes sure the barrel is held by the whole extension and not just the front face of the extension.

NB - before anyone pops along and rants about how you should not put loctite on the barrel nut THREADS.....exactly right.  Not what we are talking about.  Coat the inside of the receiver where it contacts the barrel, and the barrel extension itself; use moly grease on the threads as per normal.  Before you put the barrel nut on, wipe away any loctite that seeps out.

I use the lapping tool from Brownelsa and  only use grease. Lock tite wount do you any good unless you want to set your barrel nut and then sometimes its hell getting it off if you want to make some changes.... If you trully want to get square then the lapping tool is the best way to go... I dont usually use it on most builds but it comes in handy when having to remove just a little off the face when a barrel nut dosent want to line up....All the rifles I have built are accurate enough but again I have not had or needed to build a Match comp rifle.

I use the lapping tool from Brownelsa and  only use grease. Lock tite wount do you any good unless you want to set your barrel nut and then sometimes its hell getting it off if you want to make some changes.... If you trully want to get square then the lapping tool is the best way to go... I dont usually use it on most builds but it comes in handy when having to remove just a little off the face when a barrel nut dosent want to line up....All the rifles I have built are accurate enough but again I have not had or needed to build a Match comp rifle.

Thanks for the replies!

I have the receiver lapping tool.  I was thinking that if the barrel extension to receiver fit had any play at all it could cause grouping issues.  One of my ARs have had  grouping issues with two separate barrels so it's going to be the guinea pig.  This all started after I talked to a friend to builds and sells high end AR's about some issues he had.  He had a Krieger barrel that he could not get to group so he sent it off to several people for testing and finally someone resorted to changing the upper receiver out and the issues went away.

What's the part number of the blue loctite?

Just the run of the mill blue loctite that you can find from any hardware/auto store - Loctite 242.

I knew someone would pop up and say that, which is why I posted in the reply above yours:

"NB - before anyone pops along and rants about how you should not put loctite on the barrel nut THREADS.....exactly right. Not what we are talking about. Coat the inside of the receiver where it contacts the barrel, and the barrel extension itself; use moly grease on the threads as per normal. Before you put the barrel nut on, wipe away any loctite that seeps out".

Excellent.  This weekend I'll also be rebarreling my 308.  Why spend $500 on a new barrel and not do everything to ensure consistent performance?

That is pretty much my outlook on it...not just with high end barrels though, even GI type ones.  It only adds about 10 mins to your install (and a little bit of extra effort come removal time), so why not.  The one I had the stringing issue with was a run of the mill Thompson Center chrome lined barrel.  The way it cured that convinced me it was a good idea for all my builds going forward, regardless of how good a fit between barrel and upper - in best case, it is just extra security and peace of mind, but in a fairly loose fit, it can make all the difference and eliminate a lot of angst and head scratching, and tweaking (and cursing!) with scope mounts, etc....