I know this has been done a lot, but I thought this works well, is easy, and cheap
(This was inspired by efforts by mikenlapaz)

Weight is 5 oz.
$10 buys enough aluminum to do 4 mufflers
Simple to build, with hand tools only

A little louder than stock ryobi muffler, but no worse than a typical chainsaw
Turns 7000 rpm on MA Classic 18x8 (single ring ryobi, circa 95)
(Have not directly compared to stock muffler, which will not fit on my motor mount)

I will post details if anyone is interested

Pete Johnson