question on bedding the barrel extension into the upper

[tdbru]

Horde,
I have this question rolling around in the back of my head. if you use Loctite products to bed the extension into the receiver, to take up all the slop, if any, what happens if you need to re-barrel? Is the assembly permanently assembled, as in glued in? does the bedding compound remove easily from both the extension and receiver? Is mould release used on one of them? How do you separate a barrel assy from the receiver without damaging the receiver if they've been bedded? And what is the best material to use for bedding?
thanks,
-tdbru

[stubshaft]

I have used Loctite red to bed uppers in the past. It can be rebarreled if you heat up the upper and use a one inch dowel to drive out the barrel. I currently use Loctite 642 (green) which I consider to be permanent with and without a shim. Rumor has it that you can heat it up and drive the barrel out but the temperature to do so might weaken the upper.

Having seen a marked increase in accuracy between barrels that were not shimmed and glued in as opposed to those that are I am willing to assemble each one as a permanent assembly. A new upper can be had for as little as $40.00.

[Old Bob]

I had an Wilson Combat barrel in a BCA side charge upper that was bedded with Loctite 620. I wanted to move that barrel to a PF upper. With the upper mounted in a vice block, I inserted a 1" diameter dowel from the rear of the upper & smacked it with a large rubber mallet. The barrel popped right out. I think that 620 Loctite kinda breaks like glass when it sets. Give it a good whack & it'll break loose. You could also warm it up a little with a propane/butane torch before you give it a smack.

The 620 residue on the barrel extension & inside the upper pretty much just peeled right off.

[41bear]

^^^^^^^^^, right on.

[A5BLASTER]

Doesn't matter what locktite you use a wooden fowl rod and hammer will drive the barrel out.

That being said, I don't use locktite anymore, I now use steel shim stock and do a heat and freeze compression fit up after I lapp the reciver. Still easly drove out when I need too but much better fit up in my opinion.

[Red*Lion]

In my recent upper build, I wrapped a cut piece of heavy duty aluminum foil (a bit under .001) and mounted. It ended up getting it to go in without any big hassles and it was a pretty tight fit without needing to use any Loctite. I do not see a point in lapping the receiver and was not possible on the Aero m4A1 enhanced upper I used on the build.

[Lemonaid]

I would strongly recommend not using red loctite. I hate it! The amount of heat required before it loosens is incredible. It is indeed permanent.

[FLshooter]

I don’t bed my AR15 barrel extensions.I just square the reciever face.Because I’ve never seen enough evidence to show that it actually helps accuracy. But I’ve seen others do it and I’ve installed barrels for others in my garage and used Loctite 620.I had to remove a couple of barrels off that were Loctite bedded . A5 Had told me to use a piece of an old mop stick. I wound up getting a 7/8 inch hard wood dowel at Home Depot and it did the trick. I held the receiver with my vice block.One or two Swift hits and it’s done.

[tdbru]

thanks Guys. good to know. i eventually want to build an upper by myself and i'll have to decide to shim or loctite. after checking the fit in the first place of course. if it starts out as an interference fit, like some, then no shims or loctite needed, just heat and cold.
thanks again,
-tdbru

[1Shot]

I second "DO NOT USE THE RED LOCKTITE". Use the BLUE medium strength thread locker. I used Permitex blue medium strength because I could not find any Locktite brand locally. You can go on YouTube and see many methods to use. Some cut strips out of aluminum pop cans to use as shims.

[Old Bob]

The Wilson Combat barrel I took out of the BCA upper had to be thermal fitted in the PF upper. The barrel was a pretty sloppy fit in the BCA upper. That's why I bedded it in the first place. In the back of my mind I was dissatisfied with that assembly & spent the money for a better upper.

[FLshooter]

The Wilson Combat barrel I took out of the BCA upper had to be thermal fitted in the PF upper. The barrel was a pretty sloppy fit in the BCA upper. That's why I bedded it in the first place. In the back of my mind I was dissatisfied with that assembly & spent the money for a better upper.

I just got a 300BO pistol barrel from Mark PF on Monday that I installed in a BCA upper. Face was true and the barrel fit snugly.I have never had a problem with BCA Parts. I’ve done quite a few builds with BCA upper receivers ,and for me,they’re just as good as any. BCA barrels suck.

[drewthebrave]

If you want to ensure a tight fit, you may want to consider using a BCM upper receiver. They intentionally size the receiver on the small side of the tolerances so that you have to heat it up to fit the barrel extension. I bought their blemished receivers at $60 and used them for my 11.5" 5.56 pistol and 18" 6.5 Grendel builds. For the first one, I held the threads over the stove, and on the second I used a heat-gun - both methods worked just fine.

However, you may have trouble truing the face, as the PTG facing tool that I have wouldn't fit in either of the BCM uppers I have. If you want a true face that's a thermal fit without buying extra tools, you might want to look at JP Enterprises or Precision Firearms billet receivers. They're pricey, but they have a good reputation.

[Klaus Von Richter]

I use loctite to bed any AR barrel I want accuracy out of. If the extension doesn’t fit tight in the upper, you will have accuracy problems. With that said, do not use 242 or 271, also know as blue or red. They are thread lockers and not right for the application. Loctite 619,648, and 680 are retaining compounds. They are made to fill in the gap on a slip fit.

You will notice a difference in accuracy by bedding a loose fit on an upper and barrel extension.

[cwlongshot]

I absolutely agree with KVR!!!

I bed every one!!

Also agree with A5Blaster. It WILL COME OUT! Its NOT THREADS its a smooth surface and Will shear the adhesion.

Its just something that always helps and never hurts so why NOT DO IT!?!!

CW

[R2BRO]

please explain to me; if the barrel is tightened to the upper with barrel nut @ 40ft-lbs, what difference does your loctite make after that?......

bedding is useless operation; feel free to prove wrong, but using mechanical engineering arguments and not your observations which can have many variables to it.

[cwlongshot]

Its your barrel dude!! Dont want it dont do it is AMERICA!! :p

Question asked and Answered. Choose to listen or just move on. Your choice. We stop learning for two reasons and two reasons alone. CHOICE & DEATH.

CW

[Mad Charlie]

What CWL said, and mechanical engineering arguments aside, I can tell you that based on fifty years of experience, if it CAN move, it WILL move, and not necessarily in a predictable or consistent direction.

What the he is wrong with squaring up mating surfaces and bedding loose fits? Does it cost too much? Is it too complicated? Does it smell bad? Will it make you late for dinner?

I just don't like leaving things on the table that have a good chance of increasing the accuracy of my weapons, and I have seen a difference. I bought a package deal from AA a couple years ago, barrel, upper, and gas block. That setup was the sloppiest fitup I have seen yet but I didn't know as much then. When assembled up it was barely getting 6" at 100. That's when I bought a lapping tool and 680 Locktite, and it did take a lot of lapping to square up. Then it started shooting into an inch or a little more, quite an improvement. Made me a believer.

[Klem]

I tried it and there was no difference in before and after groups.

The barrel came out easily however I chose a Loktite designed to do that. To be fair, it was a tight fit to start with and sub MOA (Lilja) so arguably there was never going to be a noticeable improvement.

I remain skeptical but open to the suggestion that it might help if a sloppy fit.

[Msalm]

I once had a discussion with a TACOM RIA equipment specialist for the then new Knight Armament M110 rifle. Knight permanently BEDDED the barrel extensions with epoxy on those rifles...it was the only way they were able to meet the Army’s accuracy requirements for that system. I personally use red locktight and BAT barrel extensions when I make AR barrels. The BAT extensions are the most square, concentric extensions I’ve ever used. I chamber my barrels through the headstock same as any precision bolt rifle and after threading and fitting the extension, indicator runout on the extension is always less than .001” on the BAT. I’ve never seen less than .004-5” on OEM extensions and as much as over .010”. So I also true the uppers also. Square and solid, it does help IMO.