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Several on this forum use Loctite for barrel bedding the barrel extension to the upper receiver after lapping the upper. I've used Blue Loctite to do so but I notice that others use Green Loctite (620). Since adhesion isn't the objective but filling the gap between the extension and upper is the objective, what advantage is there in using Green Loctite, if any? Green Loctite would make the barrel more difficult to remove because of its greater adhesion properties. I did read somewhere that Green Loctite (620) has greater expansion properties and presumably would be better at gap filling especially with cylindrical devices.
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I used the 620 Loctite on the original upper receiver for my Grendel AR. It was a BCA upper & had a sloppy fit with my Wilson Combat barrel. I replaced it with an upper from Precision Firearms. The same barrel was a thermal fit in the PF upper. It didn't take a lot of effort to remove the barrel from the BCA upper. I put a 1" hard wood dowel in the upper & then gave the dowel one good whack with a dead-blow mallet. The 620 Loctite pretty much shattered & the barrel came out easily. What Loctite remained on the barrel extension just peeled off. 620 is for this sorta thing - cylindrical fittings at high temps. Blue (242/243) is a medium strength thread locker. It's bond can be broken using regular hand-tools. I wouldn't recommend using it for bedding a barrel.
I refuse to be victimized by notions of virtuous behavior.
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Do yourself a soild and forget the glue.
Get you some steel shim stock and use it to do a heat and freeze compression fit up after lapping the upper.
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Stay away from the green. It flows and it gets into every nook and cranny there is. I've been using gasket sealant ever since it was recommended to me by a tech from Proof Research. Indian Head, Permatex, whatever brand they have at your local auto parts store. Fills the gaps, doesn't make the barrel too hard to remove and cleans up easily with a little acetone.
Let's go Brandon!
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I tried Loctite 641 a while back but it never improved group sizes. It's designed to fill voids in tight cylindrical gaps and harden with almost no bond strength, so you can remove it later.
The fit was already tight so not needed in the end. It was more an experiment to see what all the talk of gluing was about. 641 does what it's supposed to do and I imagine it would improve things if the fit was more sloppy.
That said, I would concentrate on squaring the upper and getting a quality fitting barrel and nut before reaching for the glue.
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Try a tight fitting upper instead. I will select the tightest out of several, and leave looser ones for 5.56/300.
Aero M4E1 threaded uppers have been the tightest thus far.
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TruLbrt Wrote:Try a tight fitting upper instead. I will select the tightest out of several, and leave looser ones for 5.56/300.
Aero M4E1 threaded uppers have been the tightest thus far.
Then you haven't been trying the really tight ones, that require thermal fits like BCM, VLTOR, Noveske or JP Enterprises.
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I have only ever used shims. I am not a believer in needing to lap an upper. I could be open to bedding using loc tite if I ever got a barrel to upper fit that was loose. I have never had a sloppy fit with most being snug and some being tight.
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Or, build from a BCM stripped upper, they're cut slightly smaller but not sure of the dimension. One of my builds I had to put the barrel into the freezer before it would seat. They are tight right out of the gate, and never felt the need to lap.
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Another vote for 620 Green.
If I agreed with you, then we'd both be wrong.
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I just make sure itÂ’s not a sloppy fit, and use the blue loctite
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Red*Lion Wrote:I am not a believer in needing to lap an upper. The uppers are fine until they're coated, it's the coating that needs to be leveled. I've personally seen two which were bad enough to cause a problem. Most are acceptable as they are, but all I assemble get trued.
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Up until my latest, I have used BCM uppers that always require a thermal fit. That process along with truing the receiver face is something I have grown to believe in. The latest, with a Precision Firearms Lilja 720 I just received from Mark last week, I utilized .001' Stainless steel stock to mate the barrel and upper. In the end, with the end result I had to freeze the barrel and heat the upper to get her together. With about 120 shots down the tube that barrel appears as though it will be hitting above my pay grade! I've done the 620 Green on one assembly with a less than tight fit on. That rifle is a Group Buy Green Mtn. 12" Grendel and is damn accurate rifle. I'd just as soon stay away from the Loctite though.
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A5BLASTER Wrote:Do yourself a soild and forget the glue.
Get you some steel shim stock and use it to do a heat and freeze compression fit up after lapping the upper. Just saw this thread. I figure I may as well contribute my experience. I used brass shim stock for my rifles that needed a little help. Brass was the only metal my local industrial shop carried in small quantity. I would have preferred steel, but I figured metal is metal. It has to be better than slopping glue on those surfaces, which will eventually just harden in any old shape you let it conform to, whether it's a good shape or not. A metal shim on the other hand, which has consistent thickness throughout, ensures that the extension has to go into the receiver perfectly straight, and stay that way permanently. I think the 0.004" shimming material worked well for me. And this was after doing a little lapping to true the end, I should also mention.
FWIW, on my uppers I did not need to do any freezing. I just blasted my upper's forward end with a Bernz-o-matic propane torch all around for a few seconds. After that I was able to tap the barrel shim-wrapped extension into the receiver.
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SDW Wrote:Just saw this thread. I figure I may as well contribute my experience. I used brass shim stock for my rifles that needed a little help. Brass was the only metal my local industrial shop carried in small quantity. I would have preferred steel, but I figured metal is metal. It has to be better than slopping glue on those surfaces, which will eventually just harden in any old shape you let it conform to, whether it's a good shape or not. A metal shim on the other hand, which has consistent thickness throughout, ensures that the extension has to go into the receiver perfectly straight, and stay that way permanently. I think the 0.004" shimming material worked well for me. And this was after doing a little lapping to true the end, I should also mention.
FWIW, on my uppers I did not need to do any freezing. I just blasted my upper's forward end with a Bernz-o-matic propane torch all around for a few seconds. After that I was able to tap the barrel shim-wrapped extension into the receiver.
Brownell's has steel shim stock...
https://www.brownells.com/gunsmith-tools...od589.aspx
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05-08-2021, 05:26 PM
(This post was last modified: 05-08-2021, 05:31 PM by SDW.)
Old Bob Wrote:Brownell's has steel shim stock...
https://www.brownells.com/gunsmith-tools...od589.aspx
Thanks. A lot of online places do, I'm sure. I wouldn't have wanted to pay $30 ($20 + tax and shipping) for a few square inches of shimming material though. The brass shim stock packet was around $4 and a short drive away. FYI, that shop did have a lot of steel shim stock, but only in 4" x 30' rolls, That's 10 lifetimes worth for me. And I needed an assortment anyway. As said, it's an industrial HW store. A real candy store for serious home-project guys. This job's already long since done though. I think the brass will work fine.
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SDW Wrote:Thanks. A lot of online places do, I'm sure. I wouldn't have wanted to pay $30 ($20 + tax and shipping) for a few square inches of shimming material though. The brass shim stock packet was around $4 and a short drive away. FYI, that shop did have a lot of steel shim stock, but only in 4" x 30' rolls, That's 10 lifetimes worth for me. And I needed an assortment anyway. As said, it's an industrial HW store. A real candy store for serious home-project guys. This job's already long since done though. I think the brass will work fine.
Ran into the same problem here... too much shim stock I'll never use. I thought about buying it, cutting it into 12" pieces & selling it but opted for the Brownell's product 'cause I was already gonna get a bunch of gun cleaning supplies. Brass has been around a lot longer than refined steel. I too think your brass shim oughta work fine.
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Last year I found a guy on e-bay selling 0.001 stainless steel shim material, I think it was between $13 and $15 for three 2"x 6" pieces. I don't know if it's still the same price now..Have not tried to use them yet. But I will need to when I take apart, lap, bed and reassemble a Grendel upper my buddy put together for me last year, Barrel was a loose fit and I asked him to bed it for me..he didn't..I just bought the tools to do my own builds including a lapping tool and a small bottle of 620. My shop is set up to build wood and fiberglass longbows and recurves So I had to buy everything but a vice.. I recently got a Core15 M4 and a Aero XL upper receiver for my first 350L build..The Faxon barrel was tight in the Aero and I would have to thermal fit the Core15 receiver. Have to use the XL Aero since the faxon 350L barrel needs Rifle ramp..
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PVBoom Wrote:Then you haven't been trying the really tight ones, that require thermal fits like BCM, VLTOR, Noveske or JP Enterprises.
This is my mindset. I usually buy a few BCM blemished uppers when they are on sale (used to be $60, lately they're $90). With most of the barrels I've used - Alexander Arms, LaRue, PSA, Anderson - the BCM receivers have been thermal fit with no play once they are set.
I had one Wilson Combat barrel that was just ever so slightly loose in a BCM upper (and very loose in Aero and KAK uppers), so I added a dab of Loctite 620 to take up some of the slop. It's probably overkill for most builds, but I'd prefer to give myself the best chance for consistency possible.
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