adding to Vanya's list, there's also ..
http://www.straightshooters.com/chat/ , which is a good one for air rifle hunters and others who are into high powered air guns.
and for match air guns there's
http://www.targettalk.org/
and probably the largest, by membership, is the airgunbbs which is based in England -
http://www.airgunbbs.com/forums/
IMO you'll be better served posting to a dedicated airgun forum. The reason being that it's rare to find people who are experts on airguns. So it's worthwhile to use forums where they congregate.