Stolen from another web site:
Up to early 2000, the most common primer composition encountered was still the lead styphenate, barium nitrate, antimony sulfide and tetrazine type. In this priming compound, lead styphenate and tetrazine are the sensitive explosive ingredients; barium nitrate provides additional oxygen to increase the temperature of the flame, and antimony sulfide acts as a fuel to prolong the burning time. Aluminum, and occasionally magnesium, can also be encountered, but mainly in the higher-powered
magnum pistol or rifle calibres.
Powdered glass was also often added to the mixture to increase the friction and to assist detonation when the mixture is crushed by the firing pin.
I don't vouch for its accuracy, but is similar to several other internet places.