I've been doing research on AR-10 / AR-15 barrel bedding (and accurizing in general) and have decided to bed my current build's barrel using a combination of 316 stainless steel 0.001 shim stock and retaining compound.

In choosing a retaining compound, I have the following goals in mind:

• High temperature tolerance/performance: The compound needs to stay put as the barrel extension gets hot.


• Low/minimum strength: The job of the retaining compound is (minimal) gap filling, not additional shear strength. I'd also like to be able to remove the barrel.


• Prevention of galvanic corrosion: The barrel extension / shim stock and upper receiver are dissimilar metals (stainless steel vs. aluminum) and will weld themselves together over time, making separation next to impossible.

I've come across what appears to be the ideal retaining compound for the task: Loctite 668

Benefits:

• Unlike all the other 6xx Loctite retaining compounds, comes as a waxy paste stick. This would make applying it evenly and not having excess go everywhere infinitely easier, especially with shim stock fitting involved.


• High temperature: Up to 400 degrees F. Not as high as Loctite 620 (450), but better than the more commonly used Loctite 609 (300).


• Consistent low/medium strength: The strength of Loctite 609 varies radically with temperature. Loctite 620 performs more consistently. Loctite 668 varies very little (~50-60% strength) across its range.

Has anyone actually used Loctite 668 for bedding a barrel? Comments/suggestions on my approach?

many bench rest type guys do it.  can't hurt for sure and can be taken off with heat later if needed. I have done it on several of my accuracy builds.

Could just buy a tighter fitting upper. The BCM uppers for example.

Dissimilar metal corrosion, I think you’re looking for problems to solve that don’t exist. I should know it’s one of my favorite pastimes