Legally you can sue him but good luck doing that across state lines for an item worth $1500. In two or three years you might get your parts back.
People have already given you good advice but apparently you balk at taking it. Identifying him here and putting public pressure on him is your best bet to get things moving, plain and simple. His screen name would be useful but isn't necessary, just post the company name and address. As noted, someone will know him.
Doing that still isn't a guarantee of getting the rifle completed or getting the parts back but at this point it should be clear that the guy is a liar and makes commitments he can't keep so you're not going to be any worse off.
My experiences with gunsmiths are the same as jmp300wsm and JSTUART. A good one who knows his stuff and meets his commitments is a rare find, I've only known four in the last 40 years. I have known a couple who really were good gunsmiths in that they knew their craft, but one loved his beer more than working on guns and the other thought he was P.O. Ackley reincarnated but wouldn't take one shred of responsibility for commitments and was a self-centered, vindictive prick. The others just put a shingle out that said "gunsmith" but they knew as much about gunsmithing as I do about brain surgery.
