The EDM (Electrical Discharge Machine) isn't new technology. GM Tool and Die shops used it in the mid to late 60's to burn out broken taps and cut hole that were otherwise hard to machine. Back then, it was a slow process, especially when removing taps, because you were burning away a lot of material. S&W is undoubtedly only doing the rifling, after having drilled a hole near or at bore size, which would speed the process immensely. The addition of chemicals to the process may speed it was well, as when we used it back in the 60's oil was used, not as an aid in the process so much, rather to clean away burnt material.
The process is extremely close tolerance, and should leave a far smoother bore than broaching does. In any cutting process like broaching, you are literally ripping the metal off the surface, no matter how little material you take with each cutter. Not all metals cut the same either. Some cut relatively clean, while others tend to cut like gum. Some grades of stainless fall into the later class while other grades of stainless (used in the nuclear reactor field) are just plain miserable to cut. But as usual, I digress.
EDM'ing and CEDM'ing should make for a smoother, more consistent bore, and represents one of those rare instances where newer is better.
