I'm not sure about current laws, but a little over a decade ago transport of firearms on "common carriers", i.e. busses and trains traveling inter-state, was prohibited by Federal law. We used to confiscate a lot of weapons at the Greyhound station doing "interstate interdiction". Those laws had to do with carried weapons, not those checked in "belly" baggage. I'd double check if I were you before heading out. But quite honestly, I'd rather hitchhike than ride a Greyhound. Safer and less smelly, to say the least.