Maryland is a mixed bag. I have not heard of FOPA violations there but I understand that State Police in Baltimore area harnessed a citizen at the tunnel just because they saw a Florida carry license in his wallet.
Unloaded and “snapped in a holster” is legal going to a range. I have heard that the Sheriff Departments ( Wicomico and Worcester Counties) will not hassle you for an unloaded firearm but State Police will.
I do not believe that Maryland has any ammo laws.
In any case here is info from the Stste Police Website:
How can I legally transport firearms within / through Maryland?
They must be unloaded, in a carrying case, holster with a flap and the ammunition should be separate. It would be best to keep the unloaded weapon in the trunk where you do not have access to it. There are further regulations but essentially you can only transport a handgun between residence, to and from a repair shop, a shooting sporting event, between a residence and place of business if substantially owned and operated by the person. For more information please contact our Licensing Division.