I'd be curious to know what the limit is here WA state...at one time I may have been over limit although I doubt very much if I am today. Still, knowing what the legal limits are would be helpful if anybody knows - I hate to think of asking the authorities...
A year or so ago the WA State Muzzleloaders Association was lobbying the legislature to get BP storage amounts increased. I think the bill failed. I just did a search and came up with a pretty detailed answer that _seems_ accurate. I checked the transportation requirement in Washington State's WACs and it matched with the requirement below. I am confident the others are current as well.
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BLACK POWDER
WAC 296-52-71075 Shipping containers. Black powder, used in muzzleloading firearms must be packed,
stored, and transported in U.S. DOT approved shipping containers.
WAC 296-52-71080 Storage.
(1) Private residence. No more than 5 pounds of black powder is permitted. No restrictions apply.
(2) Private car. No more than 5 pounds of black powder is permitted. No restrictions apply.
RCW 70.74.340
Small arms ammunition, primers and propellants — Transportation, storage and display requirements.
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.