When I go to the US, taking a firearm and trying to get it through customs there is an effort not worth the trouble. Bringing your guns to hunt in South Africa it is a formal but easy procedure and may take 20 minutes of your time, if that.
Because firearms are not formally registered in their owners' names in the US (informally they in fact are, as everybody knows!) the South African authorities need your personal confirmation that any firearm being brought into the country in fact legally belongs to the person who carries it. This is to prevent illegal weapons entering the borders.
This statement is used to have your rifle entered into the South African firearms register and to issue you with a temporary South Africa firearms licence on the spot. Now you can take your firearm anywhere like any other citizen without any interference by anyone as long as you keep it under your control, or locked in an approved safe with somebody.
To make it easy for the hundreds of US hunters who fly out to South Africa, the U.S. Customs and Border Protection (CBP) Form 4457 – “Certificate of Registration for Personal Effects Taken Abroad” is used to confirm ownership of firearms on top of whatever other personal assets you declare there . Inexplicably the CBP went and put an expiry date on this form for whatever reason some bureaucrat had conceived at the time. Lately a number of hunters from the US have made the declaration of legal ownership on Form 4457 without seeing that the form had in fact gone past its use-by date. The date of validity had expired.
You can be as sure as daylight that another bureaucrat halfway across the globe who sees that your firearm ownership statement carries a date that says that the form you used had formally expired will (and not unreasonably so) assume that the form is not valid anymore, and the firearm will remain in custody until you return to the USA.
Hunters visiting South Africa (or Europe and Australia) please insist that the U.S. Customs and Border Protection bureaucrat hand you a form that will not expire during your stay in the foreign country.