.004" will give .016" increase to the ball diameter.
9 pound "Onion skin" was closer to .0015", I thought.
Simplicity patterns (fairly cheap) if very thin. I used it in a .45 3 1/4" rifle I had once a-pon-a-time.
For a paper ctg. you want enough strength to work. The really thin paper is too much that way, I would assume. I could carry
my ctgs. in my parka pockets all season without damage. I did this as a test.
Having a tapered paper ctg. made orientation easier as well as easier inserting into the muzzle (I found). Too, it resulted in less powder loss after tearing off the powder end.