From the back cover:
"Guns! Guns! Guns! (3G for short) lets you design custom firearms for any role-playing game. Design realistic weapons in a universal format, and convert the stats to the system you like best. Choose from conventional weapons, rockets, lasers, particle beams and railguns. East to follow directions and step-by-step design sheets guide you through each aspect of custom weapon design.
"And, you can design weapons at any Tech Level where they are possible, not just when they historically appeared. Want to give the Romans machine pistols? Or, design lasers for WWII? In 3G, if it could have been done, you can do it!"