As long as you understand that this is a fundamentally AWFUL idea... I guess I can check all my Western guides.
AA#2 is the fastest burning powder in the accurate line and you are talking about the colossal magnum hamdgun round that uses arguably the slowest burning powder in the history of handgun ammo.
Using the fastest powder in the largest, high pressure handgun round is literally the best possible chance you can actually have for catastrophic detonation.
Okay, the Western/Accurate 5.0 guide shows one reference to a publication date -- August, 2013.
This guide actually lists three .500 Mag loads using AA#2, all with a Ranier plated slug, the 275, the 300 and the 335gr plated slugs.
275gr start 23.0gr max 27.0gr 55k psi
300gr start 21.7gr max 25.6gr 54.6kpsi
335gr start 20.0gr max 23.5gr 55k psi
They show no loads at all for AA#5 or AA#7, both of which are faster powders than AA#9 and slower than AA#2.
In my opinion... yes, you are barking up the wrong tree.
At it's most basic, a fast burning powder will reach peak pressure quickly, long before it builds velocity comparable to a proper powder. It does this all the while giving absolute FULL PEAK PRESSURE. It's basically all the wear and tear and less performance and when the pressure curve is plotted on a graph, it is a violent, pointy, horrible fast rise, it's the polar opposite of linear and predictable. Messing with fast powders in high pressure and large cases is where you go from "mild" to "meltdown" with very little warning.
In my opinion (we all have them) the only thing you gain is a lower charge weight (economy?!) and it allows you to get rid of AA#2.
It's better used in 9mm, .38, .44 Special or .45, add those up and you have like 60 published loads.
I like to swap brass... and I'm looking for .32 H&R Mag, .327 Fed Mag, .380 Auto and 10mm. If you have some and would like to swap for something else, send me a note!