Five states including Florida, Illinois, Texas, Montana and North Dakota accounted for nearly half that total.
Alabama is the latest state to outlaw Glock switches. A law signed this month by Republican Gov. Kay Ivey makes possessing parts designed to convert pistols into machine guns a felony punishable by up to 10 years in prison.
The bipartisan push in Alabama came after police said they believed conversion devices had been used in fatal shootings, including one in September that killed four and injured 17 people outside a Birmingham lounge.
Democratic New Mexico Gov. Michelle Lujan Grisham signed a law in February making possession of a weapon conversion device a felony punishable by up to three years in prison.