Publius, the feds are denying Schrader firearms by claiming he is a prohibited person, as defined in 18-922(g)(1) which says that anyone convicted of a crime to which a sentence of more than a year can apply, is a prohibited person.
Until 2007, MD did not have any maximum sentencing laws for misdemeanors. Then, a bill was passed that made most misdemeanors have, as a maximum, a 3 year sentence. Including the misdemeanor assault charge that Schrader was convicted of.
The feds are applying the current State law to the 40 year old conviction.
In essence, post McDonald, the plaintiff is claiming an ex post facto application of the law which denies his fundamental right.
It is clear, that any State may change (by statute) the nature of a misdemeanor crime to include a sentence of more than a year (one year and one day, anyone?), and the way the feds will interpret 922(g)(1), you become a prohibited person, regardless of when the crime was committed.