From the back cover:
"More Guns! takes over where 3G3 leaves off. It does the design work for you, and provides complete stats for over 500 guns and melee weapons for eight separate rpg systems... It is truly a weapon supplement from Hell.
In addition, the conversoin rules for each system have been expanded for even more detail, with numerous examples and technical notes to provide inspiration for your own 3G3 custom designs and conversions. Now it's even easier to do it all, with 3G3 and More Guns!"