Loctite

[rcoodyar15]

Actually, this would be a bad thing. The upper does nothing but hold part in place. Threading the barrel directly to the upper would unnecessarily complicate installation and would not hold the barrel assembly as securely. Remember, the upper is made of aluminum. You would be then be using aluminum threads. Threading the barrel into the aluminum threads will lead to the barrel squirming in the upper

can't thread the barrel into aluminum. The barrel extension is steel for a reason. yes the upper supports the barrel. Imagine the leverage a 26" 5.5# barrel has on that receiver.

[lysander]

Just because companies or builders do something, doesnt mean it works. Doesnt mean it causes harm, either.
For one, if they charge $10, or $20 or more to put half a dozen drops of loctite on a barrel extension, they are making a good profit on it.
So, if the barrel extension can and is moving about in the receiver, then yes, loctite will fill that space. However, most loctites get somewhat hard, even brittle, when cured. Aluminum grows faster than steel when heated. Larger diameters grow more than smaller ones. This means that the diameter of the receiver bore will grow faster, and more, than the barrel extension. Loctite will not stop this. What this amounts to is that the loctite will crack, and become not attached to the receiver bore, and likely not attached to the extension either over time. Some may even work its way out into the bolt carrier area.
Interference fit of the two parts will accomplish more, as the initial growth will not at first loosen anything, until the growth exceeds the amount of interference fit.
Really, of you got almost .004" of slop in the fit, youre probably better off wrapping the extension with a piece of shim of either brass or steel, to get a tight, tap in fit.
If the loctite does anything, the cushioning effect on the harmonics is probably the most.
Anytime the receiver must be heated to install the barrel, adding loctite is pointless. The receiver will cool and push it out before it has time to fully set up.
Some loctite versions are softer than others, so maybe some builders are hoping the softer versions will crack and seperate less.

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Not saying that Loctite© on your extension is a good or bad thing....

I do know a bit about anaerobic methacrylate-based adhesives. They are pretty good at handling different rates of thermal expansion, provided the diametrical difference doesn't get to big, about .001" to .002".

How hot would your upper have to get to have the 1.000 inch bore grow .001"?

Interesting question, the aluminum bore is a thick walled tube, and partially contained by the steel barrel nut, so, the aluminum bore under the nut won't increase in diameter more than the barrel nut. You are not going to see a change in the diametrical clearance between the upper and the barrel extension at temperatures less than 350°F - 400°F, and at these temperatures, the Loctite© will break down anyway.

BUT, the Loctite© doesn't disappear, it will still take up space acts a shim.

Yeah, I can see how it might help, but, like facing off the front of the upper, the improvements will be very small, and most people won't see ant difference unless they are shooting off of a machine rest on a concrete pad...

[MistWolf]

can't thread the barrel into aluminum. The barrel extension is steel for a reason

As you know this already, why do you keep advocating threading the barrel directly to the upper?

[rcoodyar15]

The anschutz 54 is known for its accuracy. It too is a .22 caliber with a slip in barrel. I have attached a link of how builders are rebarreling these actions. Kind of interesting.

http://www.rimfireaccuracy.com/Forum...l-installation

[Gunfixr]

A 22lr and a 5.56 isnt going to be a very close comparison.
Looks like the anschutz is normally pinned, not clamped in with a barrel nut. Also, recoil is different. Heat will be less.


Loctiting on the ar may do something for some. It wont fill large gaps and stay. It wont be present if there is no gap. Its still a glue, and compressible. The thicker it is, the more compressible it is. How much the metal expands has been said to be very little, and of no consequence, 001" or less. However, this thread is about filling just such a space to try for more accracy, so apparently, it is of consequence to somebody.
We are down to minutia (sp?) here as it is, unless you are putting together a top of tolerance receiver with a bottom of tolerance barrel extension. At that point, there is room for a metal shim, which is always more solid than a plastic glue.
But, metal wont absorb harmonics, just transfer them.

I seriously doubt it does very much. As pointed out, enough to be noticed by the majority of shooting conditions.

Threading it in does complicate things, but they can be overcome. Other rifle systems have threaded in barrels that do line up correctly. However, the steel threaded into aluminum issue remains.

Really, all of this skips the fact that the thinnest, and likely weakest point is the section of receiver behind the threads, where it is undercut. The barrel extension goes only a little past this point, not enough for any glue to stabilize any flex of that section.
I dont know of any tests offhand to see about flex in that section, but it is the thinnest part of the equation. The reverse barrel nut receivers have way more material at the barrel/receiver junction, would be noticeably more rigid.

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[lysander]

A 22lr and a 5.56 isnt going to be a very close comparison.
Looks like the anschutz is normally pinned, not clamped in with a barrel nut. Also, recoil is different. Heat will be less.


Loctiting on the ar may do something for some. It wont fill large gaps and stay. It wont be present if there is no gap. Its still a glue, and compressible. The thicker it is, the more compressible it is. How much the metal expands has been said to be very little, and of no consequence, 001" or less. However, this thread is about filling just such a space to try for more accracy, so apparently, it is of consequence to somebody.
We are down to minutia (sp?) here as it is, unless you are putting together a top of tolerance receiver with a bottom of tolerance barrel extension. At that point, there is room for a metal shim, which is always more solid than a plastic glue.
But, metal wont absorb harmonics, just transfer them.

I seriously doubt it does very much. As pointed out, enough to be noticed by the majority of shooting conditions.


Threading it in does complicate things, but they can be overcome. Other rifle systems have threaded in barrels that do line up correctly. However, the steel threaded into aluminum issue remains.

Really, all of this skips the fact that the thinnest, and likely weakest point is the section of receiver behind the threads, where it is undercut. The barrel extension goes only a little past this point, not enough for any glue to stabilize any flex of that section.
I dont know of any tests offhand to see about flex in that section, but it is the thinnest part of the equation. The reverse barrel nut receivers have way more material at the barrel/receiver junction, would be noticeably more rigid.

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Well, some people are on a Holy Quest to make a 0.1 MOA rifle...they'll try anything, I suppose.

[762x39]

This fellow in his book recommends Loctite for a match AR: "The Competitive AR15 Builders Guide" Book By Glen D. Zediker

Clint McKee (Fulton Armory) Does in his book also

[cst]

I use blue on my Grendel build too..after a 1000 rounds,about 400 suppressed I took it apart...had to use some heat gun but there was still plenty of loctite there.. I cant tell if it makes a difference but the gun was a 1/2 moa build so I can't tell if it worked but it doesn't hurt anything to try it... but I would never put on the threads like KAC

[RogueUSMC]

I remember once that I said a prayer before I built a rifle. It did some amazing feats and the accuracy was pretty solid.

Nice!