Rick, I have been scammed also, but this is what I did. And it works.
!) contact the Attorney General of PA fraud division. File a formal complaint. They will investigate right away. Especially with a firearm.
2) If you mailed it fiale a report with the USPS inspectors office.
3) File a report with your local police and the PA police in the city of the seller.
4) As it was done on the internet, call the FTC an file a fraud complaint. They only act if there is more than one complaint. But it is a start.
By filing the police reports you make your position stronger. Filing a false police report is a crime in its self. I also told the AG office that I did this and reminded them that it is a crime for filing a false report.
You may not get you funds back, but it will scare the he?? out of the seller.
Good luck Mark
"Three people can keep a secret as long as two of them are dead" Mark Twain