In the N-SSA, and ACWSA, all the shooters use what is called "cap plugs". They are perfect for .58 cal minnie type balls. I use them for all my muskets. They are made of plastic.
Now, if you are thinking of loading 60 or more grns of powder, they might not be the best, because, about 60 grns is about the max load you can get in them along with the inverted minne.
You put your powder charge in them, insert a properly sized minne ball, then dip the minnie skirt in the lube of your choice. You could then use a zip lock bag to keep extra rds in, while hunting. I carry my musket caps in my pocket while hunting.
When new, I take a small needle and pierce the "cap plugs". this is to let air out of them so you can insert the minnie, or some times, the minnies will pop out, specially when being jarred aound.
Hope this helps
Dave