If you are a Maryland resident and you lawfully own the grandfathered gun, you can transport it. See page 14, lines 9-16.
An out-of-state resident cannot bring in a post-ban rifle, even for a one-day shooting competition or whatever.
http://www.mdshooters.com/showthread.php?t=114585
I used to be a resident of MD, and still own a home there (never sold it). However, several years ago, I bought a house in WV and became a resident of this wonderful mountainous state. No longer an official resident of MD.
So, then, even while still owning a house & land in MD, I cannot bring firearms from WV to my other home in MD? I guess I can't take my firearms back-and-forth as I reside at one home or the other?