upland bird hunting, you can only have no more than three rounds loaded
The gun cannot be " capable" of holding more than three shells. It the plug is out and you are checked, you'll most likely get a ticket.
WDFW regulations on page 24 of the Washington State Migratory Waterfowl and Upland Game Seasons
Firearm Regulations
IT IS UNLAWFUL TO HUNT:
•
Game birds with a shotgun capable of
holding more than three shells.On page 31 of the same book Federal Regulations state:
Below is a summary of the most commonly
violated federal regulations. Federal
regulations related to migratory bird hunting
are located in Title 50, Code of Federal
Regulations, Part 20.
For a complete list of federal regulations
pertaining to migratory bird hunting, prior to
going afield hunters should visit the U.S. Fish
and Wildlife Service website at
www.fws.gov/hunting.
No persons shall take migratory game birds:
b) With a shotgun of any description capable
of holding more than three shells, unless it is
plugged with a one-piece filler, incapable of
removal without disassembling the gun, so its
total capacity does not exceed three shells.State is going to take precedent, since it makes no reference to a filler I would say the Fed rule does not apply.