RE: ever make a muffler?
If I were attempting this, I'd use phosphor-bronze brazing rod. I've used it for refrigeration tubing and it never fails. You could get it at a wholesale house that deals with heating/cooling. It takes a lot of heat but bonds brass or copper perfectly. You have to get copper just to the point of red hot to get it to flow, at that point it bonds and is self fluxing.