I keep a .357 lever action carbine in the back of my truck. It is 100% legal, and carried in a case. If the law were to stop me, I have no problem with that, as the first thing I do is hand them my CCW and tell them I'm carrying on my person anyway.
In DC, it may be different, as my beloved Arizona laws won't protect me there.
However, my little carbine is accurate to at least 100 yards, and if got the opportunity to pop a shot off at the "Beltway Murderer" (I refuse to give in the the media brainwash and call that ****bag a sniper), I wouldn't hesitate.