several people were selling them on eBay last year
pretty simple slip on PVC tubes stuffed with aquarium filter floss
many Paintball guns are open bolt so alot of sound exits the rear of the action
The BATF has a specific note on Paintball Silencers
let me look...
http://www.atf.treas.gov/firearms/faq/faq2.htm#a9
(A9) Q. Are Paintball and/or Airgun Sound Suppressers legal? [Back]
A. §921(a)(24) The terms "firearm silencer" and "firearm muffler" mean any device for silencing, muffling, or diminishing the report of a portable firearm, including any combination of parts, designed or redesigned, and intended for use in assembling or fabricating a firearm silencer or firearm muffler, and any part intended only for use in such assembly or fabrication.
Numerous paintball silencers tested by the Firearms Technology Branch have been determined to be, by nature of their design and function, firearm silencers as defined in 18 U.S.C., Section 921(a)(24). An individual wishing to manufacturer a firearm silencer must receive prior approval from ATF by submitting an ATF Form 1 and paying a $200 making tax.
If I have any further questions as to this classification, who should I contact?
Please send a written request to our Firearms Technology Branch at the following address:
Bureau of ATF
Firearms Technology Branch
650 Massachusetts Avenue, NW
Room 6450
Washington, DC 20226
see also:
http://www.corin.com/bill/paintball/silencer.html