This video is based on these instructions from instructables:
https://www.instructables.com/Tin-Can...

!!! USE A LOT OF ELECTRICAL TAPE, SO IT WONT LEAVE SCRATCHES ON YOUR BELL!!!

It's not nearly as versatile as a real Harmon mute, but it works exceptionally well as a practice mute. It reduces the sound level a lot without causing too much resistance to the playing. Actually, it works better than most of the commercial practice mutes I have tried.

Sadly, I accidentally screwed up this mute by trying to push it into the bell of my pocket trumpet, which had a little different shape. After that it didn't work that well anymore in my normal B&S Challenger 3137.

Don't pay too much attention on my playing, I made this video some time ago :D