I've read through this entire thread and found it very interesting and informative. Couple months ago I started to shop for my first cap and ball revolver, an 1858 Remington replica. I recently found one, a Uberti replica, in stock at Midway. About the same time I started to shop for this gun I learned about the percussion cap shortage and ordered the .22LR cap maker. That was several weeks ago and still haven't received it. If I ever receive it I will certainly try some of the advice given in this thread about doubling up on the can material, etc.
Meanwhile, your post back in March picturing plastic tubing around what appears to be a cap or possibly a primer mounted over a percussion nipple leads me to some questions about which you and other members may have knowledge. Couple weeks ago I saw a youtube.com video about using vinyl tubing to mount a small pistol primer over a percussion nipple. I have tried it and it works great with one big exception. Once the primer is fired after the hammer strike I can't cock my revolver for another shot. It turns out, after much troubleshooting, the hammer needs to fall and rest closer to the frame before the hammer/trigger mechanism can be cocked again. The pistol primer stands off the nipple about 1/16" to perhaps 3/32" too far and prevents my hammer from falling far enough for the hammer mechanics to work. At first I thought the primer was jamming against the frame behind the cylinder(breech face?) and preventing cylinder rotation. In fact the cylinder rotates freely with the primers mounted on the nipples.
So, now I am wondering if I could file down the nipples 1/16" to 3/32" inch and thereby allow the primer to be mounted closer to the chamber and allow the hammer to fall as far as it needs to in order to be cocked again. Of course, like you, I don't want to blow myself up or ruin my gun. Opinions please . Thanks.