I have seen this a few times. The FFL gets it with the firearm, but has to keep it. Just like Atlantic Arms receives 30 and more round mags all day and sells them to people out of Maryland through the mail. They even have Beta-Mags for sell, just not to us.
http://www.atlanticfirearms.com/storecategory97.aspx
Maryland Criminal Law Code 4-305(b) states…
“A person may not manufacture, sell, offer for sale, purchase, receive, or transfer a detachable magazine that
has a capacity of more than 20 rounds of ammunition for a firearm”
This section does not apply to a .22 caliber rifle with a tubular magazine
so that doesn't apply to ffl's? he would be in violation of two things.. recieving it and then offers it for sale. i read it as you can't offer it for sale from a maryland based location regardless of where actual transfer takes place but thats only because its so cut and dry then again i guess that would make some of our classified ads i mean i know the ways around our law (pa & va gunshows, shipping to out of state address) and all that but i didn't think anyone would actual ship one here, even on gunbroker people take the time to say no hi cap mag sales to md blah blah so it just strikes me odd that they actually sent a 30rnd to maryland.