I never had much luck with Aluma Black no matter what I did. The color was never better than a mottled dark gray and was not very wear resistant Aluminum is fundamentaly different from steel in that it developes a tenacious oxide film in seconds if the bare aluminum is exposed to oxygen.

If you don't want to have the frame re-anodized, then one of the high tech gun paints is probably a better choice. I have used Brownells Aluma-Hyde II on several Ruger 10-22's with satisfaction. It takes about a week for full cure, but once cured it is tough and very solvent resistant. Other paints or coatings that require baking are even better.

In case you want to fully restore the original finish, it can be re-anodized for not much money.

Welcome to US Anodizing is one firm( there are others) that can apply either Type II or III(hard) anodizing. I don't know which was orginally used on your revolvers, but either one is an order of magnitude better than any other finish you might put on in a home shop.