I wanted to remove the permattached Brake from a CAI CETME, and install a Flash Hider. I didn't see anything that looked like they'd drilled into the Brake, so I assume it must've been Silver Soldered on. Would a propane torch work ??? Or would the heat damage the barrel ??? Any suggestions ???

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ATF spec was to use 1,100 degree solder or higher.  Thus, a propane torch will take forever, if it will work at all.  Remember that it doesn't matter how hot the flame gets, the metal has to get to the proper temperature, and that will take forever without a really hot flame.  Steel is a good conductor of heat.

However, I suspect that many brakes were poorly put on using solder paste, and what sometimes happens in this case is that flux simply starts acting like threadlocker rather than getting a silver bond.  As soon as you heat it up to 5-600, it might melt this, and come loose.  YMMV...

If it didn't hurt the barrel installing it, it won't hurt it un-installing it.

It really depends on which type silver solder was used. Some silver solders melt at approx 1000† F, some at 1450†F and, some in between. I'd try a MAPP gas torch instead of propane.