Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
Thermo-fitting is the better approach. Loctite is a band-aid.
Any barrel can be thermofit to a receiver.
Thermal fitting is more than just heating the upper and cooling the barrel. If the fit is loose at room temperature, then you need shim stock. Wrap the barrel extension with shim stock to a few thousandths over the ID of the upper. Then barrel in the freezer, heat upper to about 200 with a heat gun. Mate the parts, let cool and viola, thermal fit. While some manufacturers use Locktite in their thermal fitting, it is not needed at all. Most thread locking compounds (including red loctite) work by a controlled oxidation process. Since the metal of AR15 receivers are passivated, that prevents the corrosion process from working as intended and in most cases, leaves a non-solidified material for a long time. The benefits are marginally better and in some cases won't help for weeks until the material hardens, and then the zero can wander.
Thermal fitting is more than just heating the upper and cooling the barrel. If the fit is loose at room temperature, then you need shim stock. Wrap the barrel extension with shim stock to a few thousandths over the ID of the upper. Then barrel in the freezer, heat upper to about 200 with a heat gun. Mate the parts, let cool and viola, thermal fit. While some manufacturers use Locktite in their thermal fitting, it is not needed at all. Most thread locking compounds (including red loctite) work by a controlled oxidation process. Since the metal of AR15 receivers are passivated, that prevents the corrosion process from working as intended and in most cases, leaves a non-solidified material for a long time. The benefits are marginally better and in some cases won't help for weeks until the material hardens, and then the zero can wander.
Thermal fitting is more than just heating the upper and cooling the barrel. If the fit is loose at room temperature, then you need shim stock. Wrap the barrel extension with shim stock to a few thousandths over the ID of the upper. Then barrel in the freezer, heat upper to about 200 with a heat gun. Mate the parts, let cool and viola, thermal fit. While some manufacturers use Locktite in their thermal fitting, it is not needed at all. Most thread locking compounds (including red loctite) work by a controlled oxidation process. Since the metal of AR15 receivers are passivated, that prevents the corrosion process from working as intended and in most cases, leaves a non-solidified material for a long time. The benefits are marginally better and in some cases won't help for weeks until the material hardens, and then the zero can wander.
Oh, I fully understand that the cure occurs in the absence of Oxygen. Oxygen is not the only oxidizer, far from it. Carbon Steels are different from Stainless steels in their place in the Galvanic series. You might call Loctite at 800-624-7767 and ask them how to successfully use their products for the intended application. I have, several times, a few of those for cases of failures. They know their product line, to include the primers and activators.
620 is gonna cook right off if you do any considerable amount of shooting with your AR.
Only if you're a bubba-bumpfire retard who likes to see your barrel turn purple and blue from the heat.
I like how none of the people who answered in a negative way have actually used this on their guns, or at least mentioned using it.
Used it on the first 20 or so AR15s I built, then was educated on it by an armorer from the AMU. Did my own research, talked to Loctite and changed methods. Carry on.
Mark
How about sharing with us less fortunate as to AMU protocol? Seems it could be of benefit to a larger assemblage here. Propriety has a place, and in the spirit of sharing, it isn’t here.
I’m sure the Co he works for wouldn’t want him sharing their proprietary method.
Ill share my proprietary method for precision AR15 rifles. Buy 5 heavy walled 7075 uppers, using a mandrel and lathe to find internal runout of the upper extensions, find the one that has the most concentricity aka least runout. Return the rest.
Once you have found a better than average one in the .001 or under range, face the extension mating surface, or lap it if you have the tool and compound. Next using a bat machine 1.000 oversize extension, turn it down so you have a tight, >.002 press fit, much of the time I heat the receiver extension to get the barrel in. Now is the time to use that 620 on the receiver extension. That is the proper way to bed a barrel according to the sources I trust.
Just an FYI... Criterion Barrels recommends Loctite 609.
Is that one better then 620 ? I don't know.... but I have used Loctite 609 on 5 barrels so far. 3 .308 AR's , 6.5CM and 1 5.56, no issues
I like how none of the people who answered in a negative way have actually used this on their guns, or at least mentioned using it.
The short answer is yes, 620 is good to go for bedding. As previously mentioned, it is for press fit applications with tolerance gap of .005 between mating surfaces. It’s retaining strength of around 4K lbs is more than adequate for helping reinforce the barrel extension/reciever extension mating especially in longer barrels. I’ve used it on all my builds since 2015, 11 in total ranging from precision 24” varmint rifles to 10.5” sbr’s. These see ever possible kind of shooting from slow benchrest firing to carbine classes to tactical shoots. The rapid fire heat has not been an issue I’ve noticed and the 2 I’ve had to disassemble have been pretty easy, just heat using a industrial heat gun and press out with a 1 ton hydraulic press. No damage to the extension or reciever. Hope this helps.