1966 Silver Dollar DD?

Keep in mind, a true doubled die is going to have a second impression which is an exact copy of the first. In this case, that's most obvious on the G - note the shape of the top serif "double." It's distinctly different from the "original," and should show the same curvature. This is impossible with Die Doubling, and characteristic of Machine Doubling.

I've never liked the term "machine doubling," because it's deceptive and inaccurate for what's actually happening when it's created. It should be more accurately called "machine smearing." But it's the term we use, so we're stuck with it.

I believe the anomaly of MD to be directly related to the speed of the strike and the accuracy of the machinery. A slower or faster strike and/or more tightly-toleranced machine parts would not allow the wandering required for this much movement during the miniscule time the die was in contact with the coin. I'm thinking a certain narrow percentage of speed setting, in conjunction with the necessary machine looseness, is the only way MD can manifest. Were it a derivative of planchet preparation, I would think we'd see a far higher prevalence of this doubling. Another consideration is, I'd think the edges of the phenomenon would be much less sharp, characteristic of metal flow rather than metal placement, were annealing to be a contributing factor.

And this is very minor movement; it just looks big because the images are big. If I've measured correctly, the maximum displacement visible in these images I measured the D) is 0.25mm. But it's even, consistent movement; the metal was physically deposited there. The retreating die just moved during the upward stroke.

Mechanical or Machine Doubling is caused by the die being slightly loose in its holder/keeper. The "smearing" does NOT occur during the actual strike ... it is the millisecond after the strike, when the press is removing the die from the planchet. If you look in any book on 'Errors", machine or Mechanical Doubling is NOT included in the "striking" section because it happens just AFTER the "strike" As soon as a floor worker tightens down the screws, the "smearing" stops and you get good clean strikes again. As the die loosens further, you will get more "apparent" offset or even a directional change. You can find many coins of the same date that have more of the design elements involved (for instance the number of letters involved)or further apparent offset on those already affected. Again, all this disappears once the screws/holders/keepers are tightened and re-aligned. There are 2 types/categories of MD .. push doubling and slide doubling.

I always wondered about Machine Doubling, thank you for sharing your knowledge on that.