Epoxy for bedding a barrel extension

[Yote Klr]

I bed all of my stick shift actions with marine tex. I use kiwi natural shoe polish as a release agent. Is there any reason I can't bed a barrel extension on an ar15 with MarineTex?

Thanks.

 

[papershredder]

What's the temperature rating of Marine Tex? Locktite 620 is the go to compound for AR barrel bedding.

 

[Yote Klr]

Yep 250 f ,not good.

I have jb high heat epoxy. Good for 550 f and 4730 psi ?

 

[papershredder]

Pressure is contained in the chamber and the barrel held on by the barrel nut so you should be ok there. If the JB is easy to break like the LT620 is, I don't see much of an issue using the JB should you ever have to remove or replace the barrel. Before bedding check the fit between the extension and receiver. If it's a snug slip fit or a thermal fit, bedding might not even be necessary at all. Whether or not bedding is necessary is a never ending debate, there's been a few threads on it. If the barrel to receiver fit is like a hotdog down a hallway, yeah shimming/bedding is recommended. If the fit is a loose slip fit but no real play between extension OD and receiver ID, then use the bedding compound at your discretion.

 

[Yote Klr]

The barrel extension is .010" smaller at the breach, snug in the front. It has slight movement, not sloppy but not tight.

 

[papershredder]

That's a hell of a lot of taper there. A shim wrapped around the breech and bedding both the shim & front of the extension would be the way I approach that.

 

[cas6969]

Yep 250 f

That's it? I know someone who repaired the head on their car's engine with it and drove it for years that way. lol

 

[Huskydriver]

Shim stock and locitite 620

 

[Cascade Hemi]

The barrel extension is .010" smaller at the breach, snug in the front. It has slight movement, not sloppy but not tight.

.010" of taper is a defective part.

 

[Darryle]

Quite using 620 when I went to thermal fit uppers.

 

[backcountryguide]

Quite using 620 when I went to thermal fit uppers.

Good for you Darryle

 

[Darryle]

Well, these clowns taught me the error of my ways, I still have a few uppers built with slip fit receivers.

Honestly, I don't know if I would be able to see an improvement in accuracy since I am the weak link in the equation.

 

[Black max]

Shim stock only, no need for epoxy or loctite.

 

[45-90]

Thermal fit....two dissimilar metals are at play, aluminum and steel barrel extension...
They do not expand at the same amount as the temperature of the components heats up....aluminum expands much faster...causing the joint between them to become looser to some degree, the more heat the looser the fit...probably affects accuracy, as things heat up, the barrel harmonics changes throughout the temperature range of the shot string.
"Something" that would insulate the joint from the steel extension to alum reciever for a longer period of time, would be a better choice, for accuracy, on longer / faster shot strings common in ARs.