You can legally own machine guns made before 1986. It requires a background check by the local LEO, a background check by the FBI, $200 to the NFA branch of the ATF and usually takes about 9 months.
There’s many, many privately owned M-16’s, HK MP5’s and AK’s in the US.
Same thing’s true with suppressors, but you can own current manufactured ones.
Ed
I don’t think our state law in Minnesota defines permissible ownership by date of manufacture.