Mattel once made a replica toy rifle. People who liked military arms made primarily of steel and walnut called the issue guns Mattel rifles.

M16's are pretty dull guns to shoot in automatic mode, and full auto rifles and carbines in general have extremely limited utility in that mode. That said, in the U.S. people should be able to own guns made prior to 1986. It's flatly unconstitutional.

To own a "post" example one would have to become a machine gun manufacturer paying a special occupational tax. That's a bit ridiculous. These days you need a storefront to do such things.