Possible.Could you rig up some sort of device using CO2 as the weapon. I've noticed that on cans of air we use to clean computers it says no not spray into your face as it may cause suffication. Have it spray on him so he can't breathe, then maybe mix in a lil bear mace for suffering's sake.
Not exactly a gun, but for Maryland wha are you gonna do?
The law basically says ANY dangerous weapon worn concealed is illegal, but the high court has said that pepper spray is not among the definition of dangerous weapons or something unless you are using it to rob someone or unlawfully injure.
If a weapon is worn openly, then it can be a dangerous weapon under state law as long as it is not worn with the intent to unlawfully injure (self defense is lawful).