I've never needed musket caps for reliable ignition. But then I don't shoot pyrodex or pellets which can require a hotter ignition for best reliability.
Pyrodex has the highest flashpoint among all powders I am aware of.
RWS Dynamit-Nobel #1075 (#11) percussion caps. Tens of thousands of shots without a single misfire because of the cap.
http://www.dnrws.com/perc_caps.html
Ted Cash cappers are also excellent.
http://www.tdcmfg.com/
Tahquamenon