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Posted: 11/27/2025 2:14:48 AM EDT
[Last Edit: Morecoffeeplease1][Edited]
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I have an upper that seems like a good candidates for this. Barrel slides right in with no resistance. Sub par accuracy as well. I ordered some 0.001 Stainless Steel shim stock. Waiting for it to arrive. Ordered a lapping tool as well but it sounds like the shimming is really what’s needed. Any advice or tips would be appreciated. Thanks Some info about it Read this a while ago in this blog and figured I’d try his method. Shame he doesn’t post anything new anymore. |
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Was that a version of this one? Hellbender's Guide From your link, I'm not fond of how far they want you to go in squaring the front of the receiver. Anywhere from 2/3 to 3/4 shiny is a nice target. Their pic is much closer to all shiny. |
Disclaimer - OP is bad at knowing things, and might catch on fire.
Vet - Op MMAMA
Every other species kills off their stupid......we cater to them. -- spin-drift
Nobody ever called 911&said I just did something smart. -- TheFlynDutchman
Vet - Op MMAMA
Every other species kills off their stupid......we cater to them. -- spin-drift
Nobody ever called 911&said I just did something smart. -- TheFlynDutchman
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The print spec for the front 1.125” of the receiver is 1.00”-1.002”. The remainder is 1.000”-1.006” Sometimes companies will try to bore it out to one diameter and the front gets sloppy. |
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Over 50 and reputed to be a formidable brigand
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Over 50 and reputed to be a formidable brigand
https://hr1871.com/
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Brownells carries the shimstock. I've shimmed some of mine and I've "bedded" with loctite others. I can't find any discernable difference between the methods. Using shims, a thermal fit worked best for me. The shim should cover the entire barrel extension, meeting at the anti-rotation pin. I use a light coat of blue loctite on the shim/extension. Heat the receiver and carefully insert the extension. You have to make sure the shim isn't "balling up" as you push it into the receiver. It's common sense, but I've seen some keep pushing as the shim wads up outside of the receiver. Not to state the obvious, but bedding or using shims will not make a bad barrel mediocre nor a mediocre barrel good. IMO, if you're going to do this, use a premium barrel only. There's no point in investing the time if you're using a rack grade barrel. |
"History teaches us that men and nations behave wisely once they have exhausted all other alternatives."-Abba Eban
"I like it both ways, but still mainly mouth it" -gonzo_beyondo
"I like it both ways, but still mainly mouth it" -gonzo_beyondo
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Originally Posted By rob78: ... There's no point in investing the time if you're using a rack grade barrel.  I got my roll of shim stock from Amazon. I don't doubt you can get it from McMaster, Midway, Grainger, or similar. The Hellbender link (I think) talks about using a Green loctite that's designed to lock slip fit parts in place. (working from memory here, please verify). |
Disclaimer - OP is bad at knowing things, and might catch on fire.
Vet - Op MMAMA
Every other species kills off their stupid......we cater to them. -- spin-drift
Nobody ever called 911&said I just did something smart. -- TheFlynDutchman
Vet - Op MMAMA
Every other species kills off their stupid......we cater to them. -- spin-drift
Nobody ever called 911&said I just did something smart. -- TheFlynDutchman
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Originally Posted By Amish_Bill: You can't discount the value or practice before you start banging away at your higher dollar parts. I got my roll of shim stock from Amazon. I don't doubt you can get it from McMaster, Midway, Grainger, or similar. The Hellbender link (I think) talks about using a Green loctite that's designed to lock slip fit parts in place. (working from memory here, please verify). Originally Posted By Amish_Bill: Originally Posted By rob78: ... There's no point in investing the time if you're using a rack grade barrel. I got my roll of shim stock from Amazon. I don't doubt you can get it from McMaster, Midway, Grainger, or similar. The Hellbender link (I think) talks about using a Green loctite that's designed to lock slip fit parts in place. (working from memory here, please verify). I just use blue for ease of release. It's better for threads. Green is preferred I believe. At the end of the day you're filling gaps around the barrel extension. They'll both work well. Good luck on your work. |
"History teaches us that men and nations behave wisely once they have exhausted all other alternatives."-Abba Eban
"I like it both ways, but still mainly mouth it" -gonzo_beyondo
"I like it both ways, but still mainly mouth it" -gonzo_beyondo
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Originally Posted By rob78: I just use blue for ease of release. It's better for threads. Green is preferred I believe. At the end of the day you're filling gaps around the barrel extension. They'll both work well. Good luck on your work. Also, Blue/Red melts or softens when hot, so it's going to keep changing its properties in a place where you want things to not change. That's why we use Rockset or Vibratite on muzzle devices and suppressors instead of Blue or Red. |
Disclaimer - OP is bad at knowing things, and might catch on fire.
Vet - Op MMAMA
Every other species kills off their stupid......we cater to them. -- spin-drift
Nobody ever called 911&said I just did something smart. -- TheFlynDutchman
Vet - Op MMAMA
Every other species kills off their stupid......we cater to them. -- spin-drift
Nobody ever called 911&said I just did something smart. -- TheFlynDutchman
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Originally Posted By FedDC: I more or less permanently bonded a barrel to an upper with JB Weld in order to accomplish the same goal. It set solid…and works fine. I can’t say it did anything magical for accuracy as it was just a standard Colt barrel, but it works fine. I wonder if putting a drop of oil on a patch and wiping it around inside the receiver until a barely perceptible film of oil were left in there beforehand, would make it able to break loose later. |
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Originally Posted By Amish_Bill: You don't use Blue or Red on the barrel threads - you use Green to fill gaps between barrel extension and upper receiver. The Green is specifically designed for this. Also, Blue/Red melts or softens when hot, so it's going to keep changing its properties in a place where you want things to not change. That's why we use Rockset or Vibratite on muzzle devices and suppressors instead of Blue or Red. Originally Posted By Amish_Bill: Originally Posted By rob78: I just use blue for ease of release. It's better for threads. Green is preferred I believe. At the end of the day you're filling gaps around the barrel extension. They'll both work well. Good luck on your work. Also, Blue/Red melts or softens when hot, so it's going to keep changing its properties in a place where you want things to not change. That's why we use Rockset or Vibratite on muzzle devices and suppressors instead of Blue or Red. I thought I said that in my post. No need to be patronizing. Yes green is preferred. No, in reality it doesn't matter. If you're cooking your barrel to 300-400 degrees, you're rapid firing at dirt clods. In that case, accuracy isn't much concern to you anyway. I've done quite a few barrels, shim, blue loctite, green loctite, shim plus loctite. They all work the same. I've found absolutely no discernable difference in how they hold up. |
"History teaches us that men and nations behave wisely once they have exhausted all other alternatives."-Abba Eban
"I like it both ways, but still mainly mouth it" -gonzo_beyondo
"I like it both ways, but still mainly mouth it" -gonzo_beyondo
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Originally Posted By Tiribulus: I wonder if putting a drop of oil on a patch and wiping it around inside the receiver until a barely perceptible film of oil were left in there beforehand, would make it able to break loose later. You would want to use some type of release agent or somthing like johnson paste wax. That being said, most of the ones I see these days are pretty tight to begin with. So much so that some of them it's impossible to even get any shim stock in. |
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Originally Posted By bpm990d: You would want to use some type of release agent or somthing like johnson paste wax. That being said, most of the ones I see these days are pretty tight to begin with. So much so that some of them it's impossible to even get any shim stock in. Originally Posted By bpm990d: Originally Posted By Tiribulus: I wonder if putting a drop of oil on a patch and wiping it around inside the receiver until a barely perceptible film of oil were left in there beforehand, would make it able to break loose later. You would want to use some type of release agent or somthing like johnson paste wax. That being said, most of the ones I see these days are pretty tight to begin with. So much so that some of them it's impossible to even get any shim stock in. The BCM M4 upper receivers are very tight. Thermal fit plus loctite is all you can do and all you need. Mega billet uppers are very similar. |
"History teaches us that men and nations behave wisely once they have exhausted all other alternatives."-Abba Eban
"I like it both ways, but still mainly mouth it" -gonzo_beyondo
"I like it both ways, but still mainly mouth it" -gonzo_beyondo
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Originally Posted By Jnat: Just to eliminate some confusion, loctite does make an actual “green loctite” made to penetrate already torqued fasteners…..not what we want here. Sleeve retainer (also green and made by loctite) is appropriate for this. It's Loctite 609 and 620. 620 is for high temperature applications. These compounds are specifically formulated to fill gaps in cylindrical joints. I do not understand why people use thread locker for "bedding" barrel extensions when it is not made for that application at all, yet a product specifically made for it exists. FWIW, I no longer use 620. If needed to achieve a press fit between the barrel extension and the receiver, I use stainless shim stock. Having used 620, shim stock, and 620 and shim stock together, I have not been able to observe a difference in accuracy between shim stock alone and shim stock plus 620. I have observed improved accuracy in uppers with slip fits rebuilt with press fits. |
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Originally Posted By rob78: . . . . IMO, if you're going to do this, use a premium barrel only. There's no point in investing the time if you're using a rack grade barrel. I disagree. I have measured accuracy gains of .58 (1.95 to 1.35) moa in 7 shot groups on a BA Modern series barrel by going from a slip fit to a bedded and shimmed press fit. I have achieved similar gains in a second Modern series barrel with just a shimmed press fit, but I can't find the exact numbers. It takes an extra 5-10 minutes to shim. |
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Originally Posted By cttb: It's Loctite 609 and 620. 620 is for high temperature applications. These compounds are specifically formulated to fill gaps in cylindrical joints. I do not understand why people use thread locker for "bedding" barrel extensions when it is not made for that application at all, yet a product specifically made for it exists. FWIW, I no longer use 620. If needed to achieve a press fit between the barrel extension and the receiver, I use stainless shim stock. Having used 620, shim stock, and 620 and shim stock together, I have not been able to observe a difference in accuracy between shim stock alone and shim stock plus 620. I have observed improved accuracy in uppers with slip fits rebuilt with press fits. |
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General education should not be mere job training, but training in how to be fully human.
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Originally Posted By FedDC: Instead or trying to shim, why not just bed it? Some form of high temp epoxy or similar would provide a 1x1 fit and address any gaps. Bedding with an appropriate material like Loctite 620 makes it difficult to impossible to rebarrel the upper. The concensus among those who have only shimmed is that it works as well as properly bedding and shimming and bedding. Rebarrelling a shimmed only receiver only requires a dowel and a hammer. |
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Originally Posted By cttb: Bedding with an appropriate material like Loctite 620 makes it difficult to impossible to rebarrel the upper. The concensus among those who have only shimmed is that it works as well as properly bedding and shimming and bedding. Rebarrelling a shimmed only receiver only requires a dowel and a hammer. Unverified: I've heard that brake cleaner (red can) will loosen green loctite if allowed to soak in. Heat will, too obviously, but 620 has the highest heat resistance IIRC. |
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Originally Posted By Jeeper21: Unverified: I've heard that brake cleaner (red can) will loosen green loctite if allowed to soak in. Heat will, too obviously, but 620 has the highest heat resistance IIRC. Disassembly requires 500 degrees. It's not going to be easy to get the material that hot. That's well above what might damage the anondizing on the receiver. Loctite also mentions using Loctite 840 for disassembly. It's not anything I'd want to get into, either way. |
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