flash hider - permanently attached to a bolt rifle barrel or not?

[Sinclair]

Does anyone know for certain whether or not a flash hider has to be permanently attached to a bolt gun barrel that is over 25.5 inches long? I am confused as to what has to be permanently attached to what length barrels and what does not. I live in the Midwest and have no plans to ever visit The Peoples Republic of California. No offense intended to you Californians, but I have cousins that live in your state and their stories raise the hair on the back of my neck! I hear Gasoline is over $6.00 a gallon! Got to raise money to give to those illegals.

Best Regards,
Sinclair