EDIT: I do question anyone's ability to "ship" an AK-47 to a country that outlaws such an item for consumer purchase. How lucky do you have to be to actually receive one with all the security in the postal services of the world these days? They open a box of cookies if I order to South Korea for god's sake.
Really? I get packages all the time. Like probably something approaching 40 in the 4 years I've lived in Korea. 2 of those have been opened by Korean customs. One of those had a bottle of advil in it that was in the box it comes from the store. The package was opened, and the store box was opened, but the bottle itself was still sealed, so they obviously weren't really all that serious about seeing what was in there.
None of these packages has ever had duty assessed.
To be at least somewhat on topic, as far as shipping guns, they probably just take it apart and ship it in pieces in different packages. Probably no laws against shipping pieces of metal, plastic, and wood around.