From back cover:
Contains a consolidated listing for every personal firearm in the basic game. Each weapon entry contains an illustration of that particular firearm, a few remarks and details for incorporating the weapon into the game.
Includes increased coverage of military and civilian rifles as well as expanded coverage of ammunition types.
Has special essays on reproduction black-powder firearms and the special low-tech auto-rifle, the M16EZ
Finally, it has a consolidated price and equipment listing for all weapons and ammunition types covered in Twilight: 2000.