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http://rimfirecentral.com/forums/index.php for the Henry. I'm not too sure about the 12ga.

Oh yea, gunbroker is the most popular, but many people stay away from there because it's become the norm to sell things at high prices. There are many places online to sell a firearm, the best being...

That is the way I perfer to do it myself, but there are many deals out there that a local shop or person can not/will not match.

Don't sell guns. Only buy.

But to answer your question, yes you need a copy of the signed FFL paperwork, and only send the firearm to the FFL. If you have any concerns about if the FFL is legit...