As much as I hate to, I agree with randian,
From wikipedia's article on ex post facto (http://en.wikipedia.org/wiki/Ex_post...#United_States
Another example is the Domestic Violence Offender Gun Ban, where firearms prohibitions were imposed on those convicted of misdemeanor domestic-violence offenses and on subjects of restraining orders (which do not require criminal conviction). These individuals can now be sentenced to up to ten years in a federal prison for possession of a firearm, regardless of whether the weapon was legally possessed when the law was passed. Among those whom the law is claimed to have affected is a father who was convicted of a misdemeanor of child abuse in connection with a spanking of his child, because anyone convicted of child abuse now faces a lifetime firearms prohibition. The law has been legally upheld because it is considered regulatory, not punitive; it is a status offense.
The mentioned decision was by the 5th circuit court of appeals, and the Supreme Court declined to hear the appeal. Interestingly, the court ruled that the 2nd amendment is an individual right, but that right was not violated by the law in question.
Where the bill up for consideration in this thread may be seen differently is that it bans classes of firearms for ALL individuals, instead of all firearms for certain individuals.