Rev. Alexander Forsyth's percussion cap used fulminate of mercury, chlorate of potash, sulphur and charcoal ie smoke producing.
Modern caps (and primers) use non-corrosive lead styphnate, barium nitrate, antimony sulfide and tetrazine, which is being replaced by non-heavy metal diazol compounds, copper boron carbide, aluminum, and potassium nitrate and proprietary stuff like SINTOX, Federal/CCI/Speer's CATALYST, Winchester WinClean & Fiocchi's lead free primers.
William Eley died in an explosion while making percussion caps with fulminate of mercury
https://londonstreetviews.wordpress...am-eley-patent-wire-cartridge-warehouse/Not sure how much fulminate of mercury or lead styphnate I'd want to inhale if not outside. Mercury vapor can cause a chemical pneumonitis and systemic toxicity. Lead vapor is also toxic.