We're playing fast and loose with the chemistry here. Substituting different primers in primers in your favorite handload is child's play compared to mixing chemicals when you don't what the expected result is.

"Oscar used laboratory grade Potassium Nitrate and a very small amount of Manganese Dioxide"
This seems correct.

"I wonder where I can scrounge up lab grade PNO3 and some MgO2?"
Well, phosphorus doesn't form nitrates (PNO3 doesn't exist) and what are you going to do with the MAGNESIUM peroxide?

"this thread says Oscar used a "very small amount of Magnesium dioxide"
No, I think it says he used MANGANESE dioxide (peroxide).
Magnesium peroxide is widely used in agricultural, environmental, pharmaceutical and cosmetic industries, but I don't think it's used in metal finishing.

"100 pounds potassium nitrate to 10 pounds of black oxide of manganese"
That would be manganese dioxide (peroxide)

"I use Magnesium dioxie (sic)"
For what? a mild bleach? You can't be using it in niter bluing because it decomposes around 660*F

"I originally used about 10% Manganese Dioxide in my mix but it went bad last year. I don't know what happen, as it started to melt a bunch of black foam kept raising to the surface."
Highly reactive oxidizers can do that. A little contamination and...FIRE!!!

"manganese peroxide is of no special advantage, safe a slight quickening of the process.""
It's a strong oxidizer and rusting is oxidation, so it stands to reason that it would give a little "kick" to the process.

"Also I have no idea what the difference in effect would be between using the Manganese Peroxide Angier mentions & the Mangenese Dioxide Oscar used would be."

None. They are synonymous. The more accurate term is "peroxide" since it denotes the oxidative nature of the chemical, but dioxide is commonly, if somewhat incorrectly, used. In manganese peroxide the 2 oygens are bonded to each other and one is readily released to oxidize other species: Mn-O-O

The term "dioxide" is more accurately applied to a chemical such as carbon dioxide where both oxygens are bonded to the carbon atom: O-C-O
Such an oxide is a considerably more stable and unreactive species than a peroxide.

"I added manganese dioxide per Oscar's formula.....I can't prove it, but the MgO seems to aid oxide growth."
I'm pretty sure you added manganese dioxide and not magnesium oxide (MgO)......but I don't really know.

Do you?