The major difference between the two varmint bullets is the internal construction of each.  The traditional Ballistic Tip® bullet has a lead core while the BTLF has a Fragmenting Copper Core™.  The Fragmenting Copper Core™ results in immediate transfer of energy upon impact due to the frangibility of the bullet. The BTLF also has a flat base compared to that of a boat tail base of the Ballistic Tip® bullet.