Legal Question in Criminal Law in California

Strict liability if it is an assault rifle that is banned: for instance, if it is fully automatic, specifically banned, has a clip larger than the legal limit of capacity, etc.

Now your question is a little short of details so that is the best answer I can give you right now. I am not sure if by "mens rea" you are saying someone has an assault rifle in there possession without knowing it. (if that is even possible).

However, unless there is something you can add, I am going with strict liability on this one.