Not sure about the policy of reviving old posts, but I just had a thought that may just work for ammonpulver in rifle casings.
I've been working with ammonpulver recently for a 1858 Remington. If you haven't used black-powder revolvers before, they can use premeasured paper cartridges to reload quicker.
These cartridges use perm papers (end papers) that you can purchase $3 for a 1000 from any beauty store. They are extremely thin and strong and also burn almost COMPLETELY, no nitration necessary. They also allow sparks to penetrate quite easily.
Why I think it might work for cartridges:
-Primers/Caps are often overpowered; The blast from primers is overkill in order to maintain reliable ignition so it will penetrate the paper fine and ignite a duplex/catalyzed load. I feel #10 caps are way overpowered as they are and they don't contain their blast nearly as well as centerfire primers.
-Provides a barrier against oxidation from the nitrate; If you corn the ammonpulver and filter out any fine meal dust, no powder should come in contact with cartridge.
It doesn't add much time to the reloading process, you just wrap around a sized dowel, use a glue stick, fold over one end, glue stick and you have a paper cartridge in seconds. Fill it up with powder, and twist the end to seal tight. The only thing I'm not too sure is if the bullet may tear the paper if seated too deeply in. You can probably have a wad to cushion it though.
So the detriments to ammonpulver are mostly resolved:
Hygroscopic- inside a sealed brass cartridge should do fine.
Wisp of smoke - not much of a problem since ammonpulver is almost smokeless, except for charcoal soot.
Hard to ignite - Perotter/Nakka's work on catalysts are very helpful. Salt/Rust are easily accessible catalysts, and duplex loads are always an option.
Grains weakening - According to Perotter/Olin's tests, 10% potassium nitrate mixed in phase stabilizes the "amidpulver" within usable ranges.
Corrosive to gun- ideally this should only be used in a beater gun. Otherwise, hot water easily flushes out any leftover remnants as they are all water soluble. Also, this article on corrosion resisting products is very comprehensive.
Corrosive to cases - Hopefully, this resolves that. However, this will require long term testing. I can't tell if any nitrates will leak through the paper, but I hypothesize this will greatly increase shelf life. If it can last a year or two, that would be enough, since any such ammunition would be long used by then.