On the advise of the great guys at AirGyro, I added washers in between the plates on the muffler to prevent them from clogging and add a SS rivet to the barrel opposite where the screws are.
Drilling the SS material was extermely difficult and I broke probably 10 bits and dulled the same number. The key was to use a slow speed and lots of force.
Next I will have the muffler spot welded to prevent the bolts coming out and going through the prop.
