I'm not sure if anyone has mentioned it, but one key is to not heat the joint directly. Heat from the bottom of the barrel so as to not burn up the flux.
Jim
Yes, mass considerations and heat control are vital to all welding/brazing/soldering applications. If you burn the flux, stop- clean it up, and start over.
JB Weld is the duct tape of epoxies (same color too-but for the quick set). It's best used for small fixes where full disassembly and proper repair can be put off for a bit, never as a fabrication method.