Doctor Doom developed this technology that can be hidden within a gauntlet of his armor. Doom can optionally include it in any of the gauntlet whenever he feels he will use it, but it is not included in the default configuration of the armor.
The Projector takes synthetic molecules and throws them to a target. As soon as the intensified molecules enter in contact with oxygen, they start growing to the size of a huge stone, becoming a deadly projectile - and at the same time, one that his quite light to carry. Doom built only one unit of the Projector, which included a supply of molecules.
Doom used this weapon to attack alchemist Diablo, who was offering an alliance. Diablo easily countered Doom's attack with a chemical compound that transformed the bounder-sized molecules into harmless feathers.
Doom also used the Projector as a weapon when Prince Rudolfo and his forces attempted a coup at Castle Doom. At that point Doom was confronting Rudolfo's alien ally the Faceless One and the later's minion Doomsman. Doom took mind control of the Doomsman and both of them attacked the Faceless One. Doom used an Electronic Energizer to nullify the Faceless One's protective force field, then attacked him with the Molecule Projector. The Faceless One retreated, only to fall in the Doomsman's grapple.
Doom later used this weapon (or one very much like it) when Iron Man invaded his castle in search of electronic circuits Doom had purloined from his warehouse. The expanding molecules momentarily startled Stark, but he was able to repel them back towards Doom and retaliate in earnest.