Wash. Rev. Code § 70.74.340
Quantities of small arms smokeless propellant (class B) in shipping containers approved by the federal department of transportation not in excess of fifty pounds may be transported in a private vehicle.
Quantities in excess of twenty-five pounds but not to exceed fifty pounds in a private passenger vehicle shall be transported in an approved magazine as specified by the department of labor and industries rules and regulations.
Transportation of quantities in excess of fifty pounds is prohibited in passenger vehicles: PROVIDED, That this requirement shall not apply to duly licensed dealers.
Transportation of quantities in excess of fifty pounds shall be in accordance with federal department of transportation regulations.
Small arms smokeless propellant intended for personal use in quantities not to exceed twenty-five pounds may be stored without restriction in residences; quantities over twenty-five pounds but not to exceed fifty pounds shall be stored in a strong box or cabinet constructed with three-fourths inch plywood (minimum), or equivalent, on all sides, top, and bottom.
Black powder as used in muzzle loading firearms may be transported in a private vehicle or stored without restriction in private residences in quantities not to exceed five pounds.
Not more than seventy-five pounds of small arms smokeless propellant, in containers of one pound maximum capacity may be displayed in commercial establishments.
Not more than twenty-five pounds of black powder as used in muzzle loading firearms may be stored in commercial establishments of which not more than four pounds in containers of one pound maximum capacity may be displayed.
Quantities in excess of one hundred fifty pounds of smokeless propellant or twenty-five pounds of black powder as used in muzzle loading firearms shall be stored in magazines constructed as specified in the rules and regulations for construction of magazines, and located in compliance with this chapter.
All small arms smokeless propellant when stored shall be packed in federal department of transportation approved containers.
RCW 70.74.340