Just to add, Destructive Devices are legal in MD, but some of them may require an explosives license as I read it. So no license needed for the grenade launcher, but a MD explosives license is probably needed for the exploding grenades.These are legal for " Law Abiding" Citizens.
CLass 3 ( NFA) items such as machineguns, destructive devices, short barreled rifles/ shotguns, Sound suppressors( silencers) and AOW ( any other weapons) are legal to own in Maryland if you meet all the requirements set forth by the State and Feds. The purchasing and transfers of these weapons are strictly regulated and are done by federally registered Class3 dealers. Authorization for transfer is screened by the Chief law enforcement official ( CLEO) before it is signed off.
BATFE then take over and process the transfer . They will also conduct additional checks. It takes approximately 4 months to process each transfer. Also, a $200 tax stamp is required for each transfered weapon.
Machineguns are also annually registered in MD.