"Assault pistols" are banned in Maryland. There are certain firearms that the state classifies as "regulated firearms" such as .50 BMG caliber rifles. Long guns with 2 or more banned features are illegal in Maryland, unless they were registered before October 1, 2013.
Some states have restrictions, banns, or require owners to register firearms they conceder to be "assault weapons". The definitions of an "assault weapon" varies widely from state to state. These definitions can include whether the gun is fully automatic, the magazine size it can carry, and others.