There were more than 4,200 requests to buy guns in Colorado on Saturday.
Susan Medina of the Colorado Bureau of Investigation says that surpassed the 4,028 background checks processed on Black Friday this year.
In 2011, CBI's InstaCheck unit set a single-day record by checking 3,031 gun buyers.
The latest surge in applications came after gunman on Friday killed 20 children and six staff members at Sandy Hook Elementary School in Newtown, Conn.
The CBI checks gun buyers against a mix of seven state and federal databases for criminal records, a process that takes less than four minutes on average.