Here's a link to documentation from the US Navy Surface Warfare Center at Crane, Indiana, summarizing the testing the Navy did on the shipping containers used for moving ammunition for the ubiquitous AK-47.
The AK-47 and its many variations are not issued to the fighting forces of the US or any of her NATO allies.
So why would the US need to ship this ammunition?
Here's one reason.
And it's not the only reason by any stretch of the imagination. But Elliot Higgins unwittingly draws a few loose ends together for us. The ammo for those Croatian AK-47s that Higgins correctly spots in his Syrian action videos obviously comes from somewhere.
My guess is it's coming in shipping containers painstakingly tested and approved by Kerry Libbert and his team twenty years ago, and it's coming in US Navy ships docking in Bahrain and Qatar and Saudi Arabia.
So the question posed here well over a year ago has at least a partial answer.