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TN, USA
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Posted: 1/26/2020 8:52:32 PM EDT
Lots of talk out there about bedding the barrel on ar builds with green loctite retaining compound. In theory I guessed it makes sense but is it actually effective? The flaw I se in doing this is that the way you go about removing something assembled with green loctite is to heat it up, usually not all that hot either as the stuff basically hardens into plastic. I used an off brands high temp line from work and noticed its operating range to be -65 thru 40* F. Actual loctites high temp was less than that. It seems to me that part of the barrel could easily get above 400* pretty soon this breaking down the retaining compound Opinions?
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KS, USA
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Posted: 1/27/2020 11:25:20 PM EDT
[#1]
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TN, USA
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Posted: 1/28/2020 2:52:44 PM EDT
[#2]
Very interesting read, I still wonder about how high temps get in the extension and how that could effect the integrity of the loctite
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KS, USA
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Posted: 1/28/2020 4:26:12 PM EDT
[#3]
Most folks don't get a precision rig smoking hot.
Dirt blasters aren't shooting precision guns. (Sweeping generalizations) Depending where you source info on Locktite 620, it shows 300-400 degrees as max. Sure it might break down some, but it would still be there. |
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TN, USA
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Posted: 1/28/2020 6:49:45 PM EDT
[#4]
Agreed on all points. I guess what I’m curious about is in a semiauto precision rig, if you take a shot say, every 5 seconds, how much heat does that put in the extension and how does the loctite react to potentially melting down then hardening back over and over again. The stuff I used has an operating range of -65 to 400* Fahrenheit. It was cool to see him talk about shims because that was one of the first things that came to my mind was to wrap half a thousandth shim around the extension along with he retaining compound. I would say your right though about the temps not getting high enough to matter
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Posted: 1/28/2020 7:16:37 PM EDT
[#5]
This may sound nuts but, if you have a barrel from a know quality maker. Try this.
Use JB Weld. It is temp stable, sets up solid and won't migrate or wear like a shim can. I mix the JB and put a thin layer around the barrel extension and then assemble the upper per the handguard instructions. JB weld is one and done so be sure of your work. I suspect you could use bedding compound also but it has a bit more shrinkage and may not stand the temps well. I have top end 10.3" barrel I will putting in an upper soon and I will use this technique. |
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TN, USA
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Posted: 1/29/2020 12:30:06 AM EDT
[#6]
I used a Wilson arms barrel in a Vltor upper and the fit was not as tight as I would have liked but I have already assembled it with the green loctite, all his came to mind after
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Posted: 1/30/2020 10:32:10 AM EDT
[#7]
Quote HistoryOriginally Posted By ErikS:
This may sound nuts but, if you have a barrel from a know quality maker. Try this. Use JB Weld. It is temp stable, sets up solid and won't migrate or wear like a shim can. I mix the JB and put a thin layer around the barrel extension and then assemble the upper per the handguard instructions. JB weld is one and done so be sure of your work. I suspect you could use bedding compound also but it has a bit more shrinkage and may not stand the temps well. I have top end 10.3" barrel I will putting in an upper soon and I will use this technique. |
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Posted: 1/30/2020 11:49:18 AM EDT
[#8]
Quote HistoryOriginally Posted By LastRites:
You may want to think about using a release agent on the inside of the receiver if the day comes and you want to remove the barrel. Kiwi neutral paste comes to mind as one type of RA. |
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USA
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Posted: 1/30/2020 4:30:34 PM EDT
[#9]
I'm building a 6.5 cm upper right now, and it's a little loose of a fit.
I'm curious if anyone has ever tried using a shim such as aluminum tape or something like that. Or does someone make a shim kit? Thanks. |
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Posted: 2/4/2020 9:01:30 PM EDT
[#10]
Rolls of stainless shim stock can be purchased in 0.0005” increments. I have a couple different sizes and wrap the extension before inserting it into the receiver. Obviously make sure the wraps are equal on all sides.
It’s cleaner and easier than glueing it in or coating the extension and milling it down in a lathe. |
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USA
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Posted: 2/5/2020 6:26:48 PM EDT
[Last Edit: rpoL98]
[#11]
under "shim stock", then "shim stock sets", then select "material" for "stainless steel"...
myself, I just buy the individual rolls instead of a set, 6" wide x 50" long, of .001" 18-8 stainless (9502K41 $13.38), .0015" (9502K63 $14.50) and .002" (9502K42 $14.54). a la carte. more than I'll ever need. https://www.mcmaster.com/shims |
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Posted: 2/8/2020 10:27:40 PM EDT
[#12]
My results have been positive.
I have gone into that info plenty. IMHO, you really have nothing to lose. My "gains" were good enough that I do it on all my assm. builds. |
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NE, USA
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Posted: 2/14/2020 5:24:48 PM EDT
[#13]
So, I've got a prior build I have apart right now. I just lapped the face of the receiver. The bbl is not threaded so I want to get that done before I put it back together. I measured the receiver ID and the extension OD and I have about .0025" difference. I thought about bedding but instead I think I'll shim it...should be able to get .001'' shim in there and still have .0005". I may have to heat the receiver a bit first but that's acceptable anyway. Two different camps here, some say loctite which has a high temp rating of only around 400 degrees, and SS shims. I test fitted everything here with a piece of .001 brass sheeting I had just to see if a .001 shim would work. Why can't I just use the brass shim stock? Brass has a melting temp of 1600 degrees, MUCH higher than that of loctite. If 400 degree max loctite is acceptable, why not brass?
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USA
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Posted: 2/14/2020 9:29:12 PM EDT
[Last Edit: rpoL98]
[#14]
nvm. my bad.
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Posted: 2/14/2020 10:41:55 PM EDT
[#15]
I’ve shimmed a few builds with .0015 or .003 SS shim stock and had great results. If starting a fresh build and you don’t wish to pay for a billet upper, BCM uppers are a good option if you want a thermofit. I just got 3 in today and they will all have to be heated to get the Rainier Arms, BCA and CLE Krieger barrels to slide in. Of the 8+ builds I’ve done with the BCM receivers the only barrel that wasn’t a thermofit was a LaRue 224Valkyrie barrel. The barrel extension was undersized/below spec iirc. I’ve had another LT stealth barrel and it didn’t have that issue, so it was probably just one that slipped through on the 224 barrel.
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Posted: 2/14/2020 10:44:33 PM EDT
[#16]
I have used Loctite 609 and 620 as a bedding compound on slip fit barrels. I allow it to set up after torqueing the barrel in place for at least 24 hours, the muzzle pointed toward the ground.
I had an upper that was a very sloppy fit to a 7.62x39mm barrel. I used Devcon Steel Epoxy and that worked well for the wider gap. None of this is necessary, but it can't hurt a thing. Stainless steel shim stock is an excellent option. Take care not to cut yourself. I always square the receiver face prior to barrel installation when using every known accuracy trick. IMO opinion, all or nothing. |
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NE, USA
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Posted: 2/14/2020 11:20:54 PM EDT
[#17]
rpol98: Obviously brass is softer than SS. That's a given. But at a melting point of 1600+ degrees it's also obviously way more solid than loctite at 400 degrees. And that's what a lot of people here are advising to use. Yes, I can get SS shim stock in 20 min at a buddy's. But "why NOT brass" over loctite? Not being argumentative but I don't see that a bbl is going to get anywhere near 1600 degrees and the brass is going to move more than loctite in any way, shape or form.
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TN, USA
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Posted: 2/15/2020 3:08:39 AM EDT
[#18]
It’s not a melting point thing, theoretically if there’s dead space in between brass shim and the barrel then the barrel could bang around and distort the shim stock also the vibration from being fired could, once again, theoretically do the same thing. Doubt it would ever be enough to effect anything tho
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NE, USA
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Posted: 2/15/2020 7:34:44 AM EDT
[#19]
I can see that point. Since my buddy's got some steel shim stock I figure on going with it. But I tried fitment with the brass and thought ''hey why not? Got to be tougher than loctite". After heating the receiver to shim the bbl, and facing off the receiver, I figure no matter what I use will be an improvement.
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