Applied VC3 Vibra-Tite on a barrel extension

[StoneHendge]

Along the likes of what Klem said - the max temp is probably when it starts to liquify and starts to lose its thread locking properties. The real reason you would put it in there is to fill any gaps when putting a barrel into a receiver is a bit sloppy (there are a lot of older threads on that), but it sounds like you had a nice tight fit to start. When it does heat up and liquify, it should actually travel to the areas where there might be gaps and fill them.

I was going to respond to your other post about VX-3 - the best place to find a good thread locker selection is an auto parts store. They're all the same across colors - red, blue, green, etc. Permatex is the brand my local guy carries.