Fifty Caliber Sniper Weapons Regulation Act of 2005 - Amends the National Firearms Act to include a 50 caliber sniper weapon (defined as a rifle capable of firing a center-fire 50 caliber cartridge) within the definition of a "firearm" regulated under that Act. Modifies the definition of "rifle" under the Act to include a weapon intended to be fired from a bipod or other support.