The ban on importing "military weapons" was for the benefit of US firearms manufacturers, which were suffering from a deluge of surplus military weapons in the '50's and '60's. Look at some of the back issues of the American Rifleman, and you'll see what I mean,

As a young Marine lieutenant stationed in Quantico, VA in 1963, I was close to Interarms' retail outlet "Ye Olde Hunter" in Alexandria, VA. On a visit there, I could not make up my mind between a Mauser HsC, a Walther P38, and a high number 1903 Springfield, each for $35.00, so I bought all three.

I still have the Springfield.