With something that big you'd be better off chopping it into pieces and shipping.
I couldn't find the specs on the web as to what type of steel is used in the barrels (go figure
) Most rifle barrels are a medium carbon steel, but I'm not sure that would be able to hold up to the heat generated by prolonged firing.
It's definitely worth at least trying to heat treat a piece to see what can be done with it. If you're buddy can cut off a chunk with an angle grinder, torch or something I'd be happy to give it a try.
There are others here who are better set up to pound out BIG pieces of steel and could even test it to see what type it is. Without knowing that, I'd just be playing with a blank until I got something that held an edge.