Hi,
It is almost pure nitrocellulose so it leaves almost no residue.
It was so easy to make that he handmade it on the cellar (no electricity for safety).
It is all in the “secret” method to make them but I promise him not to tell it. Sorry.
You can use it alone in underhammer guns but need some BP as a primer in capslocks.
He offered them in .50 only as he also made .50 underhammer rifles and pistols and a curious three barreled underhammer carbine..
If you are interested in some information I can try to translate one of the articles I wrote about.
This is how it burns.

This is the residue.

Thanks
Martin

PS: this is not much traditional. Sorry.LOL