Electrochemical Machining/Erosion for rifling a barrel

[Bavarianbrit]

Now I fancy a .303 British but with Whitworth rifling.

 

[Brad93]

I have watched it in process (slow) and that was for for large plastic injection moulding tools which I was involved with, they the toolmakers had to have a few of the carbon shapes ready as they as you say wear away.
How a carbon pin 22-28 inches long can be held to the centre axis of a tiny bored hole also beats me.

The barrels will already be gun drilled straight (within the tolerance that barrels already are), so what you'll have is a smooth guide in front of the die to keep the cathode concentric which the bore