With regard to Eric's accurate post, most of the St. Louis area "BATF Gun Busts" were for selling post-1898 guns off-paper without meeting the fed or state requirements. And most of the prosecuted cases involved HANDGUN SALES in violation of BOTH Missouri and federal laws.
Missouri law historically has required a sheriff's permit for handgun purchase. However, that law was recently terminated by the state legislature, with much assistance from the NRA.
I don't know of any locals prosecuted for selling a few personal long guns. Generally, Missouri is a gun-friendly state, and law enforcement personnel don't harass gun owners.
Jerry Goldstein