Silencers can be made from a wide variety of simple materials including aluminum cans, bubblers or soakers used on garden hoses, oil filters, pvc pipe, sprinkler risers, clog busters (used for unclogging drains, and garden tractor mufflers. There are others as well.
A good book on this topic was written by George M. Hollenback: Workbench Silencers. However, to quote Mr. Hollenback: "...putting anything on the end of a gun to reduce its noise level is a federal offense, even if it's just a pop can or plastic soft drink bottle."
That's why I'm surprised at Ron's statement:
"Finally, Here in Idaho you can purchase a silencer and use it at the range if you pay the transfer fee etc. It is not uncommon for
folks to cap marmots with silenced .22's... keeps the noise to a minimum."
Ron, what is a transfer fee?
In Finland, silencers are commonplace (although I've only recently found out that it is illegal to carry a knife in Finland--and this in a knife culture!) and it is considered to be polite to shoot your guns using a silencer so as not to disturb your neighbors.
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Hoodoo
There's no fool like an old fool. You just can't beat experience.
D.O. Flynn