I use rolls of adding machine paper and it works very well. I roll the paper into 6 feet long strips in a wall paper pan and hang them up to dry on a horizontal line with clothes pins. Using single sheets of 8 1/2 by 11 paper is a big waste of time.
I make sheets from the nitrated paper that is long enough to make a double thickness tube.
The result is a very strong cartridge. If someone asks me how durable the round is, I throw one on the ground. They never come apart.
First you do not need to use hot water; cold will work. Stir the water - potssium nitrate mixture as you add the saltpeter. When you get enough saltpeter that some settles out in the bottom of the pan, adding more saltpeter will not make a difference.
Making sure the paper is wetted completely, on both sides is important. If you use rolls of printer paper in a wall papering pan, you can start by putting some paper in one layer, then folding the paper, and folding again. So each strip is about 6 feet long. As you put each strip in, make sure it is wetted by pushing down the paper into the water as you fold it . This is easier than it sounds. I put in about 8 strips, each 6 feet long, before hanging any to dry.
Take strips out and hang them on something like a clothes line. Use a clothes pin on each strip to hold in to the line. Double the end of the strip by folding it over to prevent tearing where the clothes pin holds the strip. Don't try to dry the strips outside. The slightest wind will tear them.
As you make the strips add more water and saltpeter.
You can check how the paper will work by taking out some small pieces to try. Light them and they should burn completely except for ash. Using these papers will leave ash or glowing paper in the barrel. I never had a paper cartridge catch fire while loading a round in the chamber. I think I have used at least 30,000 paper cartridges without a problem.
I make cartridges that are cut off by the breechblock.
Use the hottest caps you can get even if you make rounds that the breechblock will cut off. It helps to prevent a hangfire, if before you fire your first shot, put the muzzle up, and tap on the side of the stock to help powder get into the hole in the breech. After the first shot there usually no problem with hangfires.