From publisher blurb:
In D&D Gamma World, weapon types are abstract: instead of saying “I'm using a longsword” and looking up the stats on a weapon list, players can describe their own weapons and then the stats are based on broad categories such as “light one-handed melee” or “heavy two-handed gun.” This offers a lot of flexibility for personalization and player choices.
However, there are still some gaps in this arrangement, whereby players can't fully define the weapons they want under the existing system. For example, what if you're using a flame thrower? A shotgun? A polearm? What about a laser pistol or a
grenade or a sonic screwdriver?
The optional system presented in this document expands the categories of weapons available and offers ways for players to change the damage types on existing and new weapon categories to
better suit their concepts.