Musket Caps, #11 Percussion caps, Flintlocks, Matchlocks, and any other primitive form of ignition are legal in Washington. In fact, this is one of the few States where it is illegal to use 209 Shotgun primers in black powder hunting guns. Musket Caps actually predate the #11 and #10 percussion caps. The old mountain men and trappers were slow to give up their flintlocks, because they were often a long ways away from a supply of percussion caps, but you could find a chunk of flint on the ground almost anywhere...