What do you mean "check in"? If its a repair or whatever, no you dont. You can even ship it accross state lines, directly to an FFL or a gun manufacturer (for waranty work, etc) w/o using a local FFL yourself. Just UPS it.
AFAIK, if you own it, its yours. If you sell it to the gunshop and you buy it back, you have to 4473 it and NICS it.
And a 12ga is the ultimate HD weapon. Birdshot inside of 10yds, 00buck outside of that.
If you could find some hollowpoints for the carbine though...
