[Jbar4Ranch]

Like load it and store it for a long period?

As an experiment, I once let a loaded and capped BP revolver go 4 full years with real black powder. The Crisco in the chamber mouths had dried up and shrunk a bit, so I smeared some new stuff on, stepped outside and all six went bang, no problem. No corrosion and no problems firing.
Black powder and subs aren't corrosive, per se, it's after the initial firing that the residue becomes very hygroscopic and attracts water like a sponge. The residue by itself isn't corrosive until it starts soaking up water out of the air.

(edit) Oh, and Pyrodex isn't "better" than black powder, or any other sub for that matter. Pyrodex came about as a substitute that could be sold by a retailer without the licensing or storage requirements of black powder, which is an explosive. Pyrodex is a flammable.