Is it legal for individuals to cross the state line and conduct a private transaction? Hypothetically does is matter if the inanimate object being sold is a bicycle,baseball cards , long gun or a handgun, if no federal laws are being violated?

Please gentlemen..I`m looking for a legal opinion..armchair Matlock`s please refrain.1229 is unenforceable,and I`m looking for who may have standing to challenge it.