And the US Supreme Court in Caetano vs.  Massachusetts (2016) unanimously declared that the Massachusetts  law was unconstitutional just last year.  

Ms. Caetano was prosecuted for having one in a domestic violence situation involving the father of her children.

"Justice Alito wrote: "if the fundamental right of self-defense does not protect Caetano, then the safety of all Americans is left to the mercy of state authorities who may be more concerned about disarming people than about keeping them safe".

https://en.wikipedia.org/wiki/Caetano_v._Massachusetts