In Washington, a semi-automatic assault rifle is defined by Initiative Measure 1639 as:
Any rifle which utilizes a portion of the energy of a firing cartridge to extract the fired
cartridge case and chamber the next round, and which requires a separate pull of the
trigger to fire each cartridge.
To purchase semi-automatic rifles as defined above, a person must be a resident of the state
and minimum 21 years of age. This restriction does not include those rifles that are:
1. Antique firearms
2. Any firearm rendered permanently inoperable
3. Any firearm that is manually operated by a bolt, pump, lever, or slide action.
There are no exceptions for military or police members under the age of 21, and .22 caliber
semi-automatic rimfire or centerfire rifles are included within the scope of the regulation.