RE: primers
 

I don't think that modifying the primer is the way to go. If you are using loose powder and not pellets, any common #11 SHOULD ignite it as long as:
1. It fits snugly down on the nipple, and
2. The flash hole is clear.
3. Your powder is dry ;)
I believe you have enough info here to make it work without doing anything to the cap. Follow the recommendations given so far and you should find the reason for your missfires.