Keith,
Browning used Dupont Imron polyurethane (an automotive poly) for years. Beretta is using something similar on some of their guns.

While I'm not totally opposed to these types of finishes, I think certain techniques like spraying on coats and usually done doesn't produce the best looking finish. Thinning a lot and sanding in a few coats then applying very thin coats of highly thinned finish with a rag, then fine sanding and polishing will give really outstanding results