is it hollow inside of is there baffles inside?
you could get some hair curlers and some felt pad and fit that inside if its just a hollow tube .
This type curlers
You could fit a few inside each other to make more of a baffle with the felt around the bigger one . Plus the odd washer that is close to the diameter of your pellet but with a few mm extra for alignment issues
thread here
http://www.airgunbbs.com/showthread....Empty-silencer