Blue Hill- I've done a lot in this area so I will relate my experience- others may have had different happenings. To start, I thought the flame of the percussion cap had to "burn through" the flamable paper to ignite the powder inside the paper case. I then did some research. Sam Colt came up with these cartridges almost as soon as he came up with the revolver. The big problem was any type case that would hold an ember- if you put powder or a paper treated cartridge into a chamber with an ember- the cartridge could explode right into your face. Colf therefore opted for tin foil for the case.
Tin foil? thinks I?? I thought the flame of the cap had to "burn through" the treated case.
The only foil I could find that was thin enough is the foil (paper backed) used to wrap some candies. Nowadays mylar might be used so the foil is hard to find. In any event I made up a bunch and VOILA! they all went off like a charm. The force of the cap was more than enough to rupture the case and explode the powder. The only problem was the foil didn't burn up very well. I loaded another round over the residue- still worked, a third round- I might get a misfire in 1 out of six rounds because the tin residue was plugging the flash hole. Forth round BIG TROUBLE- there was so much residue that I got the conical about 2/3rd of the way in but there wasn't enough room to seat it. I couldn't pull it out and I couldn't rotate the cylinder because the end of the conical was sticking out.
Well Sam Colt ran into the same problem. He ended up using nitrated fish gut but today cigarette paper works fine. I have used blank newsprint which is three times thicker than the cigarette paper and the cartiridges will still ignite from rupture. The purpose of the nitrate treatment is to burn up the residue so that it cannot hold an ember. BUT even with cigarette paper- still look in the chamber to make sure.
In any event I don't know where this idea originated that you had to tear open a paper cartridge but it is not needed.
Besides the fun of fooling around with this ammunition it also works out well as originally intended- a convenient source of ammunition. Rather that packing a flask, bullet bag, etc along on a trip- just take an altoid can of combustible cartridges.