Sounds like a great excuse for a new rifle. Any of the calibers mentioned will kill your elk. I would spend that much money on components, cleaning patches, and possibly a good trigger. Then try to shoot 100 rounds a month from all different positions. Get in the best shape of your life and...
Hydrogen peroxide, murphy’s oil soap, and rubbing alcohol works well for real black powder. Don’t know about the substitutes. Store this in a dark container like Greyfox said. Vinegar Windex & water seems to work well, but haven’t personally used it to clean a rifle with. I did use it to clean...