Berdan primed non-corrosive I got from Sportsmans Guide.
STD's function on a very well known, extensively implemented, scientific principle (I should call it aerospace technology for marketing, but I respect my customer's intelligence too much). While it might not be possible to eliminate the flash, it should be possible to reduce it. The geometry is wrong on the .30's for this much gas. What's interesting is how much further out the fireball is with the STD vs without.