I went to a gun auction sat. they had about 140 guns from an estate and there were about 7 or 8 custom gun that the owner had built from 98 mausers.He had been a gunsmith for the army at a local camp that closed years ago. While looking at the custom guns I relized they did not have serial numbers so I asked the auctioneer how they could transfer the guns whitout serial numbers. He told me they had a guy with an FFL and he would transfer them as C&R's. My question is this leagel?