The Assault Weapon Ban of 2018, which has practically ZERO chance of passage in the current Congress, would grandfather all "semi-automatic assault weapons" lawfully owned as of the ban's enactment.
Semi-automatic pistols with a detachable magazine outside the grip, like AR/AK pistols, would be considered "assault weapons" under the bill.
After the ban would become effective, grandfathered weapons would still be able to be sold...but 90 days after the ban would go into effect a FFL would have to take possession of the "grandfathered semi-automatic assault weapon" and perform a NICS check on the buyer before transferring possession of it.