I have made my own snap caps for years with great success.
Deprime the case of your choice, I clean the deprimed pocket with acetone, fill the primer pocket of case with Shoe Goo (available at Wal
mart, and lots of sporting goods and shoe stores). It will take at least two applications with a toothpick. Trim any excess. Fire away!
When the detent in the Goo starts to show, another dab of Goo will Doo.