Sounds like a pretty bogus situation for law enforcement.
There is no law against possessing a million rounds of ammo if so desired.
And some trumped up, alleged restraining order is not grounds to sieze anything without a public hearing and due process.
Lately there has been a lot of focus on confiscating or limiting the amount of ammo one can purchase and it is nothing more than a back door to gun control.
I would like to know more about this story than the article gives.
Call your local fire dept and ask them. You will more than likely find a restriction on how much powder you can have in a residential area without a permit from the fire dept and you’ll need a separate storage facility away from the house.
Guess you have never been to Kalifornia.