And in the case that you quote, Eddie Bishop Jones clearly broke the law because he did not surrender his firearms to the operator of the common carrier NOR did he provide written notice of the firearms shipment or transportation. He did not do either one.
I am not saying you can just carry your weapon onto a train and travel from state x to state y. You cannot do that, by federal law, it is illegal. All I am saying is that if AMTRAK or Greyhound wanted to be able to allow passengers to transport their firearms with them, they could do so, legally, just like airlines do. The fact that you cannot transport your firearm with you on AMTRAK or Greyhound is not Federal Law, it is company policy.
If AYZ Airline company can allow you to transport your firearm, using legal methods to do so, then so could AMTRAK or Greyhound, there is NO FEDERAL LAW prohibiting it, their company policy is what prevents them from transporting firearms just like AYZ Airline does.
Federal Law allows you to check your firearm with the operator of the carrier. It is AMTRAK and Greyhound company policy that they do not accept that.