Do a search on the forums, I think here in the engine section, and some one did an excellent thread on how to make a muffler out of sheet aluminum using only hand tools, and I think he uses a .35 RH in the photos. Really a neat and ingenious method that I want to try some day. If it's not, it should be one of those threads pinned to the top of the section. Check it out.
Good luck and have fun,
Dan McEntee