Microfusion Breeder

 or MF breeder is a type of ammunition in Fallout: New Vegas.

Characteristics
A specially designed kind of energy cell that is unique in that it is not a physical object that can be gathered like other ammunition. Found only in Recharger weapons, these energy cells replenish their reserves over time, essentially providing infinite ammo.

Weapons using this ammunition

 * Recharger rifle
 * Recharger pistol

Appearances
Microfusion breeder ammo only appears in Fallout: New Vegas. and only if you can locate one! on second run through, near end of game, not found one yet!

Behind the scenes
From the name it is likely to be associated with breeder reactors, which are a type of nuclear fission reactor that is able to produce more fissile material than it uses.