Guys, I hate to be a wet blanket, but silencers require a federal tax stamp. Federal felony to make, possess, or sell one without proper BATFE paperwork and background check. And they consider the home-made soda bottle and PVC pipe ones as illegal silencers, too. Not worth a twenty year jail term in federal pen. Also, most state game departments forbid use of silencers while hunting even if you have one legally. Game violation to use one. I can't answer about air guns, but get caught with something taped to the end of your firearm that muffles it and you will be charged with a felony. In these states, silencers are illegal period by state law and the federal tax stamp won't help: California, Delaware, District of Columbia, Hawaii, Illinois, Iowa, Massachusetts, Michigan, Minnesota, New Jersey, New York, Rhode Island, and Vermont. Note Hawaii is one.