So.. you loaned your friend money.. with no real 'date' to pay you back just 'when he could'.. now you're upset that he hasn't paid you back, but is enjoying his life.. I'm guessing w/o you being invited out?

The item purchased really is not relevant, unless it was purchased through an FFL in your name. Because a receipt would show you as the purchaser, and in turn you would have loaned the weapon to him for whatever purpose. Which he is now refusing to return, and it could be considered theft. If it was a private sale w/no record of who it was sold to, and he handed over the money..

You see where this is going.. you're better off taking it as a loss and a lesson. Any attempts w/o his knowledge and consent, of removing property from him is just going to get you into shit.. Go ahead.. enter his home when he's not there, remove a firearm... see where that gets you. Explain that to the LE/ATF/Judge as you're wearing an orange jump suit..

As has been said.. it's your word vs his right now. w/o any proof.

Oh .. and can I borrow some money to buy something...

Take it as a loss and a lesson.