KABillyMac,
I'm a law student so I can give you quick advice on this classic torts case. The short and obvious answer is yes, the gun is registered to you, it was sold without your knowledge, it's called conversion of chattels. Basically even if T's uncle believed that when he purchased the gun that it was not stolen, it doesn't change the fact that he is a converter. He did not have title to the property (gun) and therefore would be liable to return the gun or pay its reasonable value. This situation is pretty similar to a case we studied in the begin of our first year, Prosser v. Keeton, it was a case of a stolen watch. I won't bore anyone with the details, but it also discusses good faith purchasers and the balance of social policy.
Now the question remains if you'd rather go medieval on this guy or take him to civil court. The choice is yours, hope all goes well
AXPAlum
