This was muddle headed of me. And I knew better if I had applied some brain sweat to the thought. When your gun dealer calls in a NICS background check to see if you are a prohibited person, and thus not allowed to purchase a gun, the gunstore is only telling the feds that "Joe Blow is here to buy a gun, is that ok?" The gov't goes thumbs up or thumbs down. They have no idea WHICH gun you are looking at (I am almost certain. Tam will hopefully smack me down if I'm off. She actually WORKS in gunstores and such.) The gunstore isn't phoning in the serial number of your desired boomstick. For all the feds know you changed your mind and cancelled the sale after the check. Kinda silly, but it's possible. If they kept these records, all they should know is "Joe Blow had a NICS check run on him 4 times since 2002 at Bob's Blastomatic Sporting Goods and Bait Shop." If the Feds got concerned about Joe Blow they have to go to Bob's and check his records to know what Joe Blow bought. That's how the Feds trace weapons.
But the State might do something different. Massachusetts might know the serial number of all of JayG's guns.
Maryland is also a stickler.
There is a nice breakdown of Maryland gun laws in About.com
Here are the important "registry" bits:
Maryland does regulate the sale, transfer, rent and possession of regulated firearms, which consist of handguns and assault weapons. A person who is not a regulated firearms dealer may not sell, rent, transfer, or purchase any regulated firearm without going through a regulated firearms dealer. Alternatively, the prospective seller/transferor and prospective buyer/transferee may complete the transaction through a designated law enforcement agency.
So no private transfers without 'permission.'
Purchase of a handgun or assault weapon from a regulated firearms dealer is subject to disapproval by the Secretary of the Maryland State Police during a seven-day waiting period. The buyer must complete an application form that is sent by the dealer or law enforcement agency to the Secretary of the State Police for investigation.
The applicant is required to provide information regarding the buyer’s eligibility to purchase or possess a handgun, and a description (including a serial number) of the handgun being purchased.
Any manufacturer that ships or transports a handgun to be sold, rented, or transferred in Maryland must include in the box with the handgun a separate sealed container holding a spent casing from that handgun. A handgun dealer must confirm compliance with this provision. A handgun dealer shall forward the sealed container holding a spent casing from the handgun that is subsequently sold or transferred to the state police.
So if you buy a handgun in Maryland, the State police have a record of that handgun's serial number, they have your name and other identification, and if it was a new handgun they have a spent shell casing. They have also given you permission after running their own check. You can be ok-ed by NICS, but the State may have some reason to deny. They don't often deny when NICS OKs, and you can appeal.
So if the feds pass a gun-registry law and it sticks, Maryland might just hand over their database to the US Justice Department, and bingo, they know about my purchases. Well, the handguns and any assault rifles, yes.