Fusion Core

A Fusion Core is a type of ammunition in Fallout 4 and Fallout 76.

Background
Standardized fusion cores were a high-grade, long-term nuclear battery used for military and commercial applications before the Great War. Used by civilians to power a multitude of devices, from automobiles, to generators, the military instead used them for warfare, supplying Power Armor and some Gatling laser models with energy. Standard core interfaces were developed across the board to allow for Power Armor frames to use cores salvaged from weapons or generators.

Standard core
The standard fusion core, used in weapons, Power Armors, and generators.

Ultracite core
A standard core with ultracite technology, this core can only be used in conjunction with a weapon adapted using the same technology, like Ultracite Gatling lasers.