The DNR statute 10-410c specifically mentions both.
As an example, 4-203 requires a handgun to be in an enclosed case or holster. No such requirement exists for a long gun.
IANAL.
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Yup. It would still be perfectly legal to carry an unloaded shotty or rifle in a shotgun rack. Unless you want to make the acquaintance of every pporly trained MDTA cop or deputy across the state probably not a good idea to do so.