Not directed at you but does anyone know if Mexico let that guy and his semi truck full of ammo that accidentally went into Mexico back in the US?
When I was serving, lo these many years ago, M-1 carbines and mortars of 60 and 81mm cailbers were commonly used in covert operations by US and indigenous troops because, while obviously of US manufacture, were in such widespread use the world over, it was impossible to trace where a given weapon had come from.
Additionally, at a gun show (horrors!) I saw a Mauser K98 rifle of WWll vintage, WaffenArmpt stamps and all, that had been captured in Vietnam in 1971.