2018 D Nickel Machine Or DD?

IMO...Yes MD

Machine Doubling reduces the devices on the outside edge of the devices. A doubled die enlarges the devices in the center of the devices:

Note on this one. A normal image over a doubled die. Note the width in the center of the devices. That is because the devices are enlarged on the die. On Machine Doubling the device is damage on the outside edges of the devices and reduces the size with the damage it creates.
On the reverse the area where the doubled dies are created is on the central area of the design:



On the single squeeze dies, that is the affected area for a doubled die. On the central areas. On the older dies with the multi hub process, the doubling was on the outer devices. Just a new area you need to check for doubled dies on the new coins.

Nice photography!



to the CCF!