The original paper cartridges for revolvers were tapered for easier insertion.
I've been considering ordering some "Flash Paper" from a magicians supply store.
From what I've seen this should work better than homemade nitrated paper.
I usually just fill a .38 Special case with powder and tape a ball on the case mouth. The cases hold just short of 25 grains of Goex FFFG.
Undo the tape, pour powder, then seat ball.