I looked a little further into NE law (I am not a lawyer) and it appears that an antique gun (manufactured prior to 1898, etc) does not require all of the paperwork, background check, etc. as a modern gun requires.
In looking further, however, it appears the Nebraska legislature defines a firearm, as it pertains to felons, as basically any firearm that is 18" longer or less. It is possible tthe antique firearm exception to Nebraska firearm law does not apply to felons.
It honestly wouldn't surprise me if AT buys antique firearms with his bad checks. Plus now he has a sidekick, BB. In some distorted reality, having her do it for him probably absolves his perception of doing something wrong.
In one of his many Iowa cases (05771 FECR240579) he owes restitution to an auction company and upon visiting their site, antique guns are apparently a specialty.
http://www.andreasauctions.com/
https://www.iowacourts.state.ia.us/ESAWebApp/SelectFrame
AT sure has a thing for auctions and antique stores specifically. Do they not verify checks? Heck, most places in my area don't even take paper checks anymore. I can't understand how he has been able to get away with the same type of theft repeatedly, especially in todays technology driven world.