I've used both copper and thin wall brass tubing in numerous of my home-made mufflers, brazed together. Never had a problem... Just don't try to use hardware store quality (Sta-Brite) silver solder. I did that once in a pinch and it melted off in minutes. Use bronze brazing rod or "honest to god" real silver solder or silver braze, but hang on to your wallet if you go for the silver products. They work great but are sold by the inch, and are very expensive!

AV8TOR