I don't believe that with steel, a crystal structure, there is any difference at all between forged and machined from solid stock. Any difference should disappear when the forging is normalized, anyway. What giving me conniptions is the idea that those $11 breechplugs that are fitted to the vast majority of guns out there are machined from a wax casting - I know that a lot patent breeches are also cast, but they cost five times as much and are supposedly x-rayed to ensure that there are no voids (whether x-rays could actually see a seam in the casting is open to doubt, I believe).
I'm hoping that I just misunderstood Mr. Bubbles. I did have a conversation a year and a bit ago with a vender regarding the kind of steel used in various kinds of breechplugs, and he made a pretty clear distinction between cast plugs and machined plugs. That might be worth following up on.