Close, but not exactly. The 6 PPC starts out as a 220 Russian. So in fact the 20 PPC is a 220 Russian necked down and blown out to a 20 PPC. Amounts to the same thing, but it's smoother to neck down a 22 than a 6. A 22 PPC or a 6 PPC bushing die can be used for resizing with a smaller bushing. If we are talking prairie dog ammo, a Wilson seater for a 22 PPC should work just fine.I would venture a guess that a 20 PPC is just a 6 PPC necked down to a 20 caliber.
Rick